I believe that some firm or other once tried to patent the colour yellow, but I’ve not be able to track this down so far. Although this sounds silly, I believe that the firm extensively used the colour yellow in all its adverts and publicity material and believe that people identified the firm’s adverts by the blocks of yellow colour used in the adverts and that a competitor could take advantage of this by using adverts with similar blocks of yellow. One can see where the firm was coming from, of course, but thankfully the attempt failed I believe.
Yellow is, in the societies that I have lived in anyway, associated with sun, well-being, summer and generally good and beneficial things. In subtractive combinations of colours, yellow, along with magenta and cyan are the primary colours. Many computer printers use these three colour. When I was researching this post I found that computer screens use additive combinations and the primary colours are red, green and blue. (“Research” is a fancy name I use for Googling for something – I usually end up at Wikipedia, so ‘caveat emptor‘!) Apparently the reason that there are three primary colours is that the human eye contains three types of cone cells, and each type is most sensitive to one of the ‘primary colours’.
Some animals have four types of cone cells and thus would see four primary colours. According to the Wikipedia article on the subject some human females may have four types of cone cells. Most placental mammals seem to have only two types of cone cells so can only distinguish two primary colours. As Wikipedia says, it would be wrong to suggest therefore the world ‘looks tinted’ to them. It would look normal to them.
I said above that the colour yellow is generally associated with positive things, like summer, warmth and other things. It is however also associated with cowardice, but I haven’t really been able to find out why. This Yahoo Answer is inconclusive, for example. The best answers, in my opinion, relate it to the ‘yellow bile’, one of the four fluids that were assumed to circulate around the human body. It was assumed that one character was determined by the balance of these four ‘humours’.
Hmm, what else about yellow? The centre of an archery target is yellow, although it is often referred to as ‘gold’ for some reason. Interestingly, in the obviously related sport of darts the centre ring is red or black. Rifle shooting, which also uses a target of concentric circles, uses only black and white, with the circles quartered and the inner circles all coloured black, the outer ones being white.
Yellow flags flown on a ship used to indicate that the vessel had a contagious disease on board. A plain yellow flag stands for the letter ‘Q’ in semaphore core and the speculation is that this was used because it was the initial letter for the word ‘quarantine’. The Wikipedia articles says that these days the plain yellow flag is used to indicate that a vessel is free of contagious disease and requests boarding for customs inspection. I had not heard of that change of meaning, but then again, I’ve not had need to raise a yellow flag! The current flag used to indicate contagious is a quartered yellow and black flag which stands for the letter ‘L’ in semaphore code.
In many cases yellow is used to indicate warnings as in ‘yellow alert’. A yellow alert is usually one level below a red alert which is usually the top level of seriousness. Generally a yellow alert means ‘avoid, take care, and be alert’. The GeoNet site currently shows a yellow alert level for the volcano called ‘White Island’ which is around 50k from the coast of New Zealand. The volcanoes on the mainland are currently quiet. Incidentally if you look closely at the Crater Floor image at the bottom right you will see Dino the Dinosaur quietly monitoring the volcano as he has done for several years.
Animals are often referred to as ‘yellow’ although it might be more accurate to describe them as ‘light brown’. Some birds, however, are definitely yellow and domestic canaries have given their name to the colour ‘Canary Yellow’. The Yellowhammer, introduced into New Zealand from Britain is a handsome bird with a yellow head breast and belly, marked with black, and with a yellowish brown back. They can form quite large flocks and are probably more numerous in New Zealand than they are back in Britain (as are many European species). The American Yellow Warbler is also a fine yellow plumaged bird.
There are some yellow animals and someone has made a collection on this web page. Most appear to be cold blooded or insects, but there are a few ‘yellow’ mammals. The mammals don’t look particularly yellow actually, but the snakes, spiders and crabs certainly are. Some albino animals (eg ferrets) tend to look distinctly yellow at times.
In autumn (fall) leaves on some trees go yellow, while species have leaves that turn red. This is because the chlorophyll which is green is lost in the autumn as the trees prepare for winter. Many flowers, like the buttercup, have yellow flowers and domestic plants like the tulip or the rose have been bred to have yellow blossoms too. Daisies also have yellow centres and I’ve seen speculation that yellow plants are the colour that they are because the pollinating insects are sensitive to that colour, which makes sense, but I’m not sure if that is the whole story, since I believe that most insects’ eyes are most sensitive to ultraviolet. The pollen that the insects inadvertently transfer from flower to flower is often yellow.
Finally to end this ramble through the colour yellow, I’ll just mention that the inanimate world also has yellow chemicals. The element sulphur is the obvious one, though some Chromates, some Iron compounds, and lead iodide are examples of yellow compounds. In addition chemists (and almost any schoolboy) who have put sodium compounds into a flame will be familiar with the deep yellow colouration of the flame that results. It’s often the first step in the analysis of a compound.