[utexaspunk]

>We cannot tell the difference between a color which is a mixture of two (or more) frequencies of light, and a pure color, whereas we can tell chords from notes. (In spite of notes having harmonics).

Wouldn't we have to be able to distinguish polarity to tell the difference?

[tsimionescu]

I don't think polarity has anything to do with this. The idea is that we can't distinguish at all between two independent light waves, one at ~600nm (red) and one at ~540nm (green), vs a single light wave at ~580nm (yellow).