On 12 May, 22:14, Tim S wrote:

Most common sort? *Well, colour blindness is an obvious case. *But
apparently a few women have 4-colour vision.

Just out of interest, what's the 4th colour?

Octarine of course!

The problem in describing it is that as language was written by people
who couldn't see it anyway, we simply don't have a word for it. I've
heard is described as being able to see a difference between "orangey
brown" and "browny orange" as distinct colours, rather than just
shades of mud.

Presumably this is why handbags and shoes come in colours like "taupe"
and "wombat's pouch", where no-one else has a clue what they mean.