More stuff on colours

Here's an idea I've been toying around with for a bit:

The Kosi language has only five colours, equivalent to English 'white',
'black', 'red', 'blue', and 'green'. The lack of other colours could be
explained by some sort of defect in the eyes. (The colours wouldn't even be
independent lexical items: the word for 'red', for example, would be a
compound meaning something like 'blood-coloured', a feature which IIRC
Pirahã has).

Is this system plausible? (I know next to nothing about such things...)

Trebor

Support the fight against the lack of choice on November 2: spoil your
ballot!