I am just posting this message after seeing a similar thread entitled "what colour is an orange in the dark". I am a firm believer in sight being purely subjective in that it is entirely possible that 2 people looking at say, an orange, will agree that its colour is indeed orange, as they both can differentiate between the wavelengths of light correctly. The interesting thing however is that one person may see the colour (in their head) as being the 'green' of the other person. This fact will not and cannot ever be proved and so I believe that you could all be going around with 'inverted' images (in terms of colour) of what I see in MY head! Crazy isn't it! What led me to FIRMLY believe this theory is that there is no evolutionary advantage in being able to visualise the same colour in each of our heads. Indeed it would be cost to try and maintain that link between individuals. This may also be the basis behind people favouring different colours. Perhaps there aren't that many favoured colours in the world but its just that what people commonly agree is red or blue may in fact be different in each persons head. Finally I would like to add that perhaps we could take it one step futher and suggest that some (or most) people can see colours in their head that others cant or have ever seen before! The thought is baffling and humbling.