Question: After learning about colour at school, I began to wonder if there isn't actually such thing as colour - it's more just how we see it individually and that a colour such as green or red or any of the colours could mean different things to different people. Maybe it is all just an illusion - do you agree, why and is there evidence?

Kevin Arbuckle answered on 10 Mar 2014:

You are right for the most part. What we call ‘colour’ is actually just our perception (how we see) particular types of light (called ‘wavelengths’ of light). It is likely that everyone sees colour very slightly differently from everyone else, and in extreme cases you might experience colour very differently, for example in colour blind people. Similarly, other species can see all sorts of colours that we can’t see and so their world looks very different to any human.

However, although what we call colour is how we see particular wavelengths of light, the light itself exists and so there is a ‘real’ thing that makes a particular colour. Because we know this and we can look at the eyes of many species, some very clever people have done some very difficult maths and figured out how other species see colour. These results are called ‘visual models’ because they let us ‘model’ (or work out using maths) how a species sees. This lets us look at something brightly coloured like a wasp or a poison dart frog and ask whether they are as bright and showy to their predators or mates as they are to our eyes. For example, in some species, you actually find that their colour pattern is camouflaged to predators but bright and showy to mates!

I hope this answers your question (with a little bit extra information), but let me know if not, or if you want more info. I guess the short answer is that colour is an illusion, but one that has a ‘real’ and understandable basis.