Re: Do some animals see only in black and white, or do all see a little colour?

Hi Geoff,

In dealing with this question, I am going to focus simply on vetebrates.

Colour blindness is a term that descibes an animal which does not have the range of colour vision that one would expect. An animal can be colour blind and still see colour. Black and white vision involves only seeing things only in shades of gray.

Animals have cones to detect colour. In mammals there are cones to detect reds, blues and greens; however humans and a few other primates are totally exceptional in possesing all three types of cones. Most mammals appear to be able to distinguish blues and either red or green (but not both). Humans which are colour blind usually have lost some of their ability to detect both reds and greens. However, they still have the ability to see blues and yellows without any difficulty.

Even those animals that can only see one colour do not see in black and white. For these animals, it is like looking at an old computer monitor which has bright yellow/green writing on a green background. There is only one colour present, but it is still a colour monitor! Unfortunately, many written resources refer to monochromatic vision as "black and white" which has created a huge misconception for many students.

At this point, you could well be asking yourself about those few people who have no functional cones and can only use their rods to see. This rare condition is called achromatopsia. Rods are normally used at night and do not sense different colours. Contrary to what most students are taught, you still see in colour at night because rods are sensitive to a narrow band in the yellow/green part of the visible spectrum. At night therefore, we have monochromatic vision as opposed to our normal diurnal trichromatic vision.

According to the THE ACHROMATOPSIA NETWORK, there are some people who do actually see in black and white. The eyes are sensitive to colour in these people, but they have lost some of their brain function in this area due to illness or trauma.

In summary,

White light is composed of many wavelengths involving several colours. It simply would not be possible to see any visible light unless you were sensitive to at least one of the colours. Therefore it is not possible for animals to literally see in "black and white" (brain disorders excepted). They have to have at least monochromatic vision.

I hope this clears up the confusion. Have a look at this excellent website about the evolution of mammalian vision.

Richard Kingsley