In the context of the Eldar army, colour schemes provide no good answer to that.
Thing is, unlike Space Marines, which usually have all units in a chapter wearing uniform colours, Eldar have Aspect Warriors that often have colour schemes independent of their Craftworld. Unless you're prepared to paint your Aspects in Craftworld colours (which I for instance would never do - too boring), colour schemes wouldn't help.
Different base rim colours are also highly detrimental to the overall cohesiveness of the army's look. For an Eldar force, which may have units wearing multiple different colour schemes, having all bases modelled and painted in the same style is particularly important.
A printed list with reference photos is a nice idea actually
Putting myself in my opponent's shoes, I don't see it being really helpful though. Personally, I'm prepared to remind my opponent of what my units are capable of as many times during the game as he needs it, and CW attributes are not too different from all other rules here (which are numerous and cannot all be remembered by a non-CWE player anyway).