This blog article (http://korystamper.wordpress.com/2012/08/07/seeing-cerise-de...) by lexicographer Kory Stamper raises some similar issues about color names in English - how does one define "cerise" or "taupe" in the dictionary, when nobody can agree on what precisely they mean (where to draw the boundary).

There is also the issue of how best to write the definition so that people can actually understand it. Webster's Second and Third New International Dictionaries included color plates (which seems reasonable!) but also gave HSB values in the Second and complex color comparisons in the Third (cerise is "a moderate red slightly darker than claret, slightly lighter than Harvard crimson, very slightly bluer and duller than average strawberry, and bluer and slightly lighter than Turkish red"). For the Learner's Dictionary, though, they used definitions like "green is the color of grass", less precise but probably still having some psychological truth - the color of grass is surely an anchor point for our concept of green.