A great many of the world's languages don't bother with different words for "blue" and "green". To speakers of such languages there apparently *is* no category difference between them, suggesting that "red", "green", and "blue" are particularities not of human vision but of some culturally conditioned ways of thinking about colour. I'll try and hound down a reference tomorrow.
Dann Pigdon GIS / Archaeologist geo cities.com/dannsdinosaurs Melbourne, Australia heretichides.soffiles.com ___________________________________________________________________