I don't know why I like yellow, I just do. Yellow makes me think of the Sun. Yellow makes me feel warm. I like everything to be yellow. I even have a yellow bedroom. Some of my favourite yellow things are the Sun, butter, noodles, Quavers, my Care Bear 'Sun shine bear', my yellow 'Hello Kitty' top, my bucket and spade, yellow felt-tips, and my yellow Pooh Bear. Because I'm Cheeky Monkey, I should like bananas, but I don't. My dad likes yellow peppers, but I only like green ones. I do like other colours but yellow is my favourite!
– An h2g2 Researcher's daughter, aged eight.

The Electromagnetic Spectrum

Light is emitted by vibrating electric charges. The frequency depends on the rate at which the charges are vibrating, so the frequency produces different types of electromagnetic (EM) waves. Certain frequencies give us visible light, which begins with red, moving through orange, yellow, green, blue and violet.

Visible light has wavelengths between 400 nanometers (the blue end of the spectrum) and 700nm (the red end). Human eyes can only see this limited range, but these frequencies are in fact only a small proportion of the electromagnetic spectrum. At the extreme opposite ends of the visible spectrum are infrared and ultraviolet, which you need special equipment to detect.

Yellow is one of the colours we can see; in the rainbow it is situated between orange and green. A primary colour, it is a good 'mixer': red plus yellow creates orange and blue plus yellow makes green.

Yellow Shades

The artist Vincent van Gogh used chrome yellow, which he mixed with other colours and pigments to create different shades of yellow for paintings such as 'Sunflowers' and 'A Wheatfield'. Some shades of yellow include (in no particular order other than alphabetical): acid, amber, apricot, blond, buttercup, canary, chartreuse, corn, flax, gold/golden, lemon, maize, mustard, old gold, pale, quince, saffron, sand, straw, sulphur and yolk.

Yellow in Outer Space

Our Yellow Star - the Sun

The Sun (our star) is very special; without it there would be no life on Earth, because light from the Sun supplies the Earth with all its energy. Astronomers have categories for different types and sizes of star. This is called the 'Spectral Classification' system. Our Sun is a 'G' (meaning 'yellow', classified according to its temperature) main sequence (it's an 'adult' star) dwarf (it's just the right size; a bigger star would have fried the Earth before life began).

Although we know that light is white, children tend to draw the Sun (and its rays¹) as yellow in artwork.

Weather forecasters on TV have been known to use little yellow Sun stickers to emphasise upcoming (they hope) hot and fine weather.

A yellow Sun was also the symbol of the short-lived African state of Biafra.

In the realm of science fiction, our yellow Sun was responsible for endowing 'Superman' with his extraordinary superhero powers.

The outer casing of the first British nuclear bomb, operational until 1970, was called Yellow Sun.

Yellow Planet

Venus, the second planet in our Solar System, appears yellow because of the clouds of sulphuric acid in its atmosphere. However, when Venus is transiting the Sun it is silhouetted, so it appears black.

Yellow Nebula

IC 2220 in the constellation Carina boasts the more popular name the Toby Jug Nebula, due to its perceived similarity to the drinking mug. This type of nebula shines by reflected light from a nearby star. The Toby Jug Nebula, which surrounds the irregular variable red giant star V341 Carinae, is unusual in that its colour is sulphuric yellow.

Yellow Galaxy

There are lots of galaxies in our Universe. Usually, the spiral galaxies are blue and the elliptical galaxies are yellow. However, volunteer classifiers taking part in Galaxy Zoo in 2007 found some anomalies, including yellow spirals!

Yellow Comet

In late 2007, an ordinary comet passed through Perseus. Normally we'd have needed a large telescope to see it, but inexplicably it had an outburst and its magnitude increased from 17th to third, making it visible to the naked eye. For a while, fuzzy yellow Comet 17P/Holmes changed the look of the constellation, thrilling and delighting professional and amateur astronomers alike.

Hitchhikers' Yellow

In The Hitchhiker's Guide to the Galaxy by Douglas Adams, the massive chunky Vogon spaceships are yellow, as are the tiny but nevertheless immensely useful Babel Fish.

Yellow in Nature

The yellow colour of leaves is due to two classes of pigments: carotenoids and flavonoids. These are present in the leaves throughout the year but masked by chlorophyll, which dominates in the spring and summer, but decays during autumn and winter.

Yellow Trees

The Golden Wattle tree aka Acacia pycnantha is an evergreen native to Australia. It is hardy and enjoys a position in full sun. There are over 500 varieties, ranging from small shrubs to tall trees. The timber is in big demand for furniture because of its beautifully patterned grain.

The acacia flower is a national emblem which appears on Australian coins. Archibald Campbell founded the Wattle Club in Victoria in 1899, and Australia even celebrates Wattle Day every 1 September.

Laburnum (aka golden chain) produces a fantastic summer display of bright-yellow bunches which are highly poisonous. Care should be taken to ensure the tempting pods are not picked and eaten by children, who may not know or understand the danger.

Yellow Flowers

Carotenoids are responsible for the yellow in buttercups (the light reflected from carotene appears yellow). Different coloured flowers are thought by some to have special meanings. The Victorians were particularly fond of this notion. Yellow flowers popularly represent friendship or unrequited love, depending on the circumstances. Yellow lilies traditionally convey thanks and joy, and yellow carnations signify disappointment or rejection. Some well-known yellow flowers are:

• Daffodil
• Buttercup
• Crocus
• Primrose
• Freesia (the yellow ones have the strongest scent)
• Sunflower
• Dandelion (before they turn into a 'clock')

Yellow Fungi

We all know that curry stains dinner plates yellow, but did you know there is a yellow-staining mushroom² called Agaricus xanthodermus (literally meaning 'yellow skin mushroom') whose crushed skin stains yellow? It's a good job there's an h2g2 Entry on stain removal! Yellow slime molds are astonishingly smart for something without a brain.

Yellow Creatures

Yellow in animals is generally a warning colour, especially when combined with black - as seen in tigers, wasps, tree frogs and salamanders. The yellow colour makes them stand out to predators, so their 'warning' to stay away had better not be an empty threat!

Another example is the yellow cane toad which has wreaked ecological havoc on Australia since its introduction from Hawaii in the 1930s. Originally intended to eradicate cane beetles that were destroying crops, this highly toxic, warty creature carved its own pathway through the bush. The toads (known locally as 'bufos') are eaten by Australian wildlife which mistakes them for native frogs, and the ingestion of their poison, bufotoxin, kills them. This is having a devastating impact and threatening some indigenous species with extinction. The toad is even endangering Aboriginal communities by killing off traditional food sources. It's not all bad news, though. Killing a cane toad and delivering it to a government-sponsored collection point earns you free beer.

Dogs

Golden retrievers are a breed of dog which make excellent guide dogs for blind and partially sighted people. Mustn't forget Old Yellow!

Horses

Horses come in a variety of shades of yellow, from dun to palomino. Some breeds, like the Norwegian fjord horse and the Haflinger, are nearly always dun. However, the real 'golden horse' is the Equus Kinsky, originally bred in Bohemia, the coat of which often has a gorgeous metallic sheen!

Fish

Many fish, especially tropical ones, come in astonishing shades of yellow.

The yellowfish found in many African rivers are highly prized by sport anglers, especially those who enjoy fly fishing.

The yellow-belly is a family of fish native to Australasia.

Yellowfin tuna like tropical temperatures but have been caught off British shores!

Birds

The goldfinch and yellowhammer are European members of the finch family.

The golden eagle is a majestic bird of prey which was once the largest UK avian predator. It is the national symbol of Mexico and appears on the country's flag.

The golden eagle enjoys protected species status in the US and UK, and most countries where it lives have some kind of proviso law enforcement in place. There are mating pairs and nests in Scotland but their locations are kept secret to protect the eggs and chicks from thieves, with the greater aim of saving these magnificent birds from extinction.

Butterflies

There are some yellow butterflies, including the Clouded Yellow and the Brimstone. 'Brimstone' means 'burnt stone', and the Brimstone butterfly is named after an old-fashioned name for the chemical sulphur, which is the same shade of yellow. And, would you like to know, the caterpillar of the Small Blue butterfly is yellow!

Snakes

There is a huge yellow snake with white markings living at The Jungle near the boating lake in Cleethorpes. On the way out you can look at photos taken of brave visitors who posed with this snake draped around their shoulders.

If you happen to be Down Under and hear someone shout 'Tiger!' you better run for your life. They're not warning you about a big pussy cat; they're already running from the eastern tiger snake.

Amphibian

A frog that is native to the Lincolnshire fens has a yellow belly, which could be the reason why Lincolnshire-born folk bear the nickname 'yellowbelly'.

Ants

Pharaoh's Ants were introduced to the UK from tropical climes.

Yellow Food

Foods are yellow due to the plants from which they were derived. Custard and mustard just happen to rhyme!

Things you spread on toast, like honey, lemon curd and butter and margarine, are a lovely rich shade of yellow.

Corn is a very versatile food. It can be eaten on the cob with lashings of butter drizzled over it, or separated and then mixed with garden peas to add a splash of colour to the usual veg dish.

Polenta is yellow cornmeal that is very versatile.

Curries are often shades of yellow unless, for example, you're having Thai green curry for a change!

The succulent yellow fruit pineapple is tasty raw and delicious cooked. Add small segments to liven up bland cottage cheese.

The best time to consume a banana in its life cycle is when its skin is yellow. If it's still green, the flesh will be bitter. If the skin has brown spots, it will be over-ripe and taste mushy. Some varieties of banana called plantain are meant to be eaten when green, but they should be cooked first.

Of the citrus fruits, grapefruit, pomelo and lemon are yellow, as are the plastic jiffy lemons which contain lemon juice for squirting on pancakes on Shrove Tuesday³. Apricots and pears are other yellow fruits.

Yellow Drinks

Advocaat is a dark-yellow liqueur with a raw egg base. Dilute it with lemonade to make a Snowball, and serve with a glacé cocktail cherry.

Other drinks with a golden translucence include whisky, cider and wheat beer.

'Amber nectar' is Australian slang for lager.

Yellow Objects

Man-made objects are often coloured with pigments or dyes which absorb light of wavelengths other than that of the colour of the object, which is reflected. Thus yellow objects reflect yellow light which has wavelengths between 585nm and 600nm.

Paints, Pigments and Dyes

Dyes are soluble, pigments insoluble. Humans have been using the natural substances around them since pre-history. Neanderthals were making use of red ochre 180,000 years ago. They would decorate their bodies and possessions, and create artwork on the walls of caves. The colouring agents were created from minerals found in rocks, but these didn't work when applied to fabrics, so a technique using dyes, which are mainly organic compounds, had to be used.

This was perfected only through trial and error. The blue indigo is a rather drab and boring shade of yellow until it oxidises when the dyed goods are exposed to air. Indigo is dissolved in urea - formerly urine, now a synthetic compound - which makes 'indigo white' (it actually looks yellow). The indigo doesn't turn deep-blue again until the finished piece is lifted out of the vat and left to dry.

The yellow pigment massicot (lead (II) oxide) was discovered in the 16th century. By the middle of the 18th century, a variety of yellow pigments were being used by artists, including orpiment (arsenic (III) sulphide) and yellow ochre (hydrated iron (III) oxide).

In 1797, the French chemist Louis Vauquelin discovered chromium while investigating a mineral called Siberian red lead spar, taken from the Beresof gold mine in Siberia. The colours of the samples of this mineral varied from orange-yellow to orange-red. We now know that the mineral was crocoite - a form of lead chromate(VI).

By 1809, a new source of this mineral had been found in the Var region of France, and it became readily available in Europe. Painters particularly liked it due to the dark lemon-yellow colour which lasted better than earlier discovered pigments. Chrome yellow is still widely used in paints and printing inks today.

Double-yellow lines are painted along roads in the UK where drivers aren't allowed to park their vehicles. The yellow pigment is 'chrome yellow', which is a form of lead chromate(VI). A rather remarkable set of double-yellow lines is the shortest in the UK.

Yellow Traffic

Quite a number of studies, dating back as far as 1959, have concluded that the human eye, and therefore someone's attention, is more readily drawn to yellow than to any other colour. This makes it the best colour for emergency vehicles as well as safety vests and hats worn in traffic. According to the Russell Ash book The Top Ten of Everything, yellow cars come last in the list of the ten most accident-prone colours (the most being black, apparently).

This could be the reason why New York taxis are yellow, but don't bank on it - they probably just want to stand out to attract more customers. Once hailed and commandeered, be sure not to let on that you're a tourist, as this human of infernal origin has been known to take advantage of those kind of visitors. The taxis in Germany are a paler yellow, but no less prone to taking the long way round if they can get away with it!

An amber (dark yellow) traffic light is generally an instruction to drivers to prepare to stop because the lights are about to change to red. When the amber light is combined with the red it means drivers can prepare to start driving again, because after that sequence comes green, for 'go'.

Yellow in Literature, TV and Film

The Simpsons were drawn with yellow skin initially to attract the attention of TV channel-surfers. Dad Homer pronounces 'hello' as 'yel-low'.

The Yellow Rolls-Royce is a film about a regal car featuring stories about three of its owners.

The Green Eye of the Little Yellow God is a poetic tale of tragic love.

The Yellow Wallpaper is a rather spooky story by Charlotte Perkins Gilman.

The yellow brick road is the path Dorothy took to the Emerald City in her search for a way home in The Wizard of Oz.

The John Wayne western She Wore a Yellow Ribbon could have sparked the whole 'tying yellow ribbons around trees' practice.

Award-winning Nigerian author Chimamanda Ngozi Adichie (born in 1977) wrote a book called Half of a Yellow Sun as a tribute to her grandfather who died in a refugee camp during the Biafran war. This was Chimamanda's second novel, and it won her the 2007 Orange Prize for Fiction.

Yellow in Music

'Big Yellow Taxi' by Joni Mitchell was meant to be a reference to the distinctly coloured taxis in New York. The lines "took all the trees, put 'em in a tree museum, and they charge the people a dollar and-a-half just to see 'em", and "you don't know what you've got till it's gone", have become immortalised by people who care about the state of the ecology of our beautiful planet.

The song 'Itsy Bitsy Teeny Weeny Yellow Polka Dot Bikini' by Brian Hyland was featured on Dave Lee Travis' programme The Golden Oldie Picture Show. In this show, the BBC made up videos for older tunes which were recorded long before the advent of video. Some of the videos were poignant; others stretched artistic licence to the limit. A few were unforgettable, as anyone who witnessed the attractive young woman attempting to leave her bathing closet on the beach to the tune of 'Itsy Bitsy Teeny Weeny Yellow Polka Dot Bikini' will attest.

The words to 'Tie a Yellow Ribbon Round the Old Oak Tree' have taken on a new cultural significance in that yellow ribbons are commonly used in the US to honour missing soldiers.

'Yellow Submarine' is the title of a song written by Paul McCartney for Ringo Starr to sing. It was part of the soundtrack to the filmYellow Submarine which featured cartoon forms of The Beatles, upsetting some fans who thought they were paying to see a Beatles' film featuring the Fab Four.

'Goodbye Yellow Brick Road' was performed by Elton John when he appeared as a guest on The Muppet Show. Elton, suitably attired in a sparkly yellow jacket with long tails, sat playing his piano and, as he sang, numerous Muppets appeared in the background either playing musical instruments or performing special Top of the Pops-type dancing.

'The Yellow Rose of Texas' is the unofficial anthem of the state of Texas. Recorded by numerous artists including Elvis  Presley, it was first a hit in 1955 for Mitch Miller. Its history predates that by a clear 100 years, though, as it was a popular marching song for troops of the Confederate army during the American Civil War.

A Few Other Songs Featuring Yellow

• 'Yellow' by Coldplay
• 'Fiery Yellow' by Stereolab
• 'Yellow Days' by Tony Bennett
• 'Yellow Sun' by Jim Capaldi
• 'Mellow Yellow' by Donovan
• 'Moon Was Yellow' by Bing Crosby
• 'Yellow Pearl' by Phil Lynott
• 'Yellow Ledbetter' by Pearl Jam
• 'Yellow Butterfly' by Scorpions
• 'Forever Yellow Skies' by The Cranberries
• 'Eighteen Yellow Roses' by Bobby Darin
• 'Under This Yellow Sun' by Tori Sparks
• 'Yellow Bird (Up High in Banana Tree)' by Roger Whittaker

Should be Yellow

Urine should be pale yellow, the colour of straw. If you notice it's red one morning, don't panic. Ask yourself if you ate beetroot the previous day. The vegetable stains some people's pee. If you haven't consumed beetroot then it's probably blood. Again, don't panic. There can be innocuous reasons for this, like joggers' bladder  (you just ran a little too fast and bruised an internal organ). The medical term for blood in the urine is haematuria. You'll need to go to see a doctor for tests to find out the cause.

Miscellaneous Yellow Things

• h2g2 Smileys (but only some of them, eg the monster is green, the cup of tea smiley is pink and the blue sad face is blue).

• The SuperLambBanana is a Liverpool icon.

• 'Big Bird' in Sesame Street.

• Yellow Pages is the telephone directory containing classified advertisements listed alphabetically under the nature of the business, service or profession. Not unexpectedly, they're printed on yellow paper.

Yellow Games

The Yellow version of Pokémon lets you have a Pikachu⁴ (he's yellow too).

'Yellow car Mini' is a game played in the back of cars on long trips. If you see a yellow car you pinch the other person while shouting 'Yellow car'; punch them with the appropriate shout for a Mini; and pretty much beat them up if you see a yellow Mini. Or, for a less violent version, it's one point for a yellow car, one for a Mini, and five for a yellow Mini. The car has to be seen by the other person (after you've pointed it out to them) to count.

Yellow-belt Sudoku is level-two. Beginners start with the extremely easy level-one (white belt), and move up as their skills improve. Black belt, at level-nine, is the last qualification prior to tackling super-tough sudokus. Perhaps we should warn that these puzzles are seriously addictive...

Yellow Around the World

Yellowstone was the USA's first national park, while Yellow Springs is a small town in Greene County, Ohio.

Yellow Mountain (Mt Huangshan) in China is well-known all over the world for its scenery. Visitors can expect to enjoy good luck following their visit, according to Chinese legend.

'Yellow River' was a one-hit wonder which hit the UK number-one spot on 3 May, 1970. The song was about a US army survivor of the Vietnam War. The title refers to the Yellow River (Hwang-Ho), the second-longest in China, which flows down to the Yellow Sea - so named for the fine yellow silt that collects in its middle course. It was performed by UK male vocal trio and instrumental group Christie, whose video showed the lads performing the song on a boat sailing up the River Thames. Christie's two follow-up singles sank without trace.

A Yellowbelly, as mentioned, is an affectionate nickname for a person who hails from Lincolnshire. There are many versions of how this moniker came to be, although no two stories as to the origin of the term are the same. The most commonly accepted is that Lincolnshire yeomanry used to wear a very bright yellow waistcoat. During the American War of Independence, the Lincolnshire yeomanry sent forces to America. These were soon dubbed the 'Yellowbellies' in the same way that other yeomanries became known as 'Redcoats', or 'Greenbacks' etc⁵. Nowadays, it's just used as a term of endearment, usually bestowed by someone born outside the area.

Yellow Flags

A yellow flag flying over a medieval city indicated it was plague-ridden and should be avoided - the 'yellow' found in heraldry is actually gold; yellow was not an accepted heraldic colour! Similarly, a yellow flag fluttering from a ship's mast denotes a quarantined vessel.

A yellow flag is also waved at competitors during motor-racing laps if there is a significant danger ahead, such as a crash. Such a policy would no doubt have saved lives during the epic chariot race in Ben-Hur.

The country flag of Uruguay is blue-and-white striped, but the top left-hand corner features a bright yellow Sun with a face etched on it, known as the Sun of May. Half of its rays are sharp and pointed, with the rest curvy and undulating. The Argentinian flag also features the Sun of May, although its rays are portrayed smaller and more softly.

In medieval Germany and Austria a yellow dress, or just a yellow kerchief (especially in some areas when combined with green sleeves), flagged up that the wearer was a prostitute. Yellow clothing or piece of yellow material was also used to signify and shame heretics as well as Jews (the latter both in the Middle Ages and later in Nazi Germany), because it was considered the colour of Judas.

Royal Yellow

In a complete contrast, yellow symbolises the royal family in Thailand, and could only be worn by the emperor in China. The Yellow Emperor, Huang-di, is referred to as the 'Originator of Chinese culture' and revered ancestor of all Chinese people. Legend has it that the Yellow Emperor, who ruled from 2698 BC to 2599 BC, is buried in the Xuanyuan temple of Emperor Huang's mausoleum in Huangling County, in north-west China's Shaanxi province. Senior Chinese leaders have taken part in ceremonies paying homage to him, even though his story is most likely mythical.

In April 2008, a new public holiday known as Qingming (Tomb Sweeping Day) was introduced. This is a festival for Chinese people to pay their respects to their ancestors. China is sometimes known as the 'Land of the Yellow Emperor'.

Yellow Mail

The colour of Deutsche Post (the German mail service) is bright yellow; its emblem, cars and letter-boxes. The French also have yellow letter-boxes, but they are more straw-coloured. The Swiss and Austrian mail services use slightly different shades of yellow.

Yellow in Sport

If a football referee flashes a yellow card at you it means you've had a warning. Any more fouls will earn you a second yellow card, which equates to an early bath - a red card. The rest of your team will then have to run their socks off covering the ground you should have, and will probably be so displeased with you that you get sent to Coventry!

Potting a yellow ball in snooker earns you two points, if potted after a red if there are still reds on the table. And so long as you don't then go 'in off' or foul your shot by potting something you shouldn't with the ricochet.

The maillot jaune (yellow jersey) identifies the race leader in the annual Tour de France cycle race.

Other wearers of yellow include students of martial arts like Tae Kwon-Do, judo and karate, where belts are used to indicate proficiency levels.

Shouldn't be Yellow

• The whites of the eyes. If they are yellow it's indicative of a liver or kidney problem.

• Grass. It's a plant, ergo it needs water, preferably rainwater.

• Teeth. Brush them!

• Fingertips and nails. Stop (or cut down) smoking and you and your lungs will be much healthier.

Bad Yellow Stuff

Some medical conditions result in yellowing of the skin, called jaundice⁶. It is caused by bile pigments in the blood, and diseases like hepatitis.

Yellow fever is a tropical disease caused by a virus that's a member of the flaviviridae family (from the Latin flavus, meaning yellow). It is spread by the bite of the mosquito Aedes aegypti.

If you're 'yellow', or have a 'yellow streak', you're considered a coward.

German people go yellow, as well as green, with envy.

Finally, a word of advice:

Never eat yellow snow!⁷