The ability to discriminate light is found in man and other primates, in certain species of birds, fishes, reptiles and insects. They have visual receptors that respond differently to various wavelengths of visible light.
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There are several theories of colour vision. More than a hundred years ago Clerk Maxwell showed that colour vision was trichromatic or based on a three-colour system.
Recent investigations of retina have shown that each cone has one of three pigments absorbing red, green or blue. The ability to see colours cannot be deduced in animals merely by finding cones in their retinas as some colour blind animals have cones! Most people will now accept that a bull is reacting to the waving of a rag rather than to its red colour. Pets are able to distinguish colours especially dogs! Experiments show that golden hamsters are colour blind, dogs and cats have a faint colour sense, giraffes can see some colours but confuse green, orange and red. Horses, sheep, pigs and squirrels can also see a few colours. Monkeys and apes have good colour vision as do most birds. Penguins and gulls prefer red! Frogs are particularly sensitive to blue light. Bees are able to distinguish six different colours! Their colour range has been pushed towards longer wave lengths than that of man! They see ultra violet but not red. A few insects do see red notably fireflies and day flying butterflies.
The colours of flowers are very closely linked with insect colour vision. Some flowers do more than attract insects by their bright colours: they guide the insects to the nectar store by radiating lines contracting with general petal colour!
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