Color is not a physical phenomenon, but a perceptual one; there are some wavelenghts that, in isolation, lead to perception of specific colors, but actually, there isn't a wavelength for any color.

For example, one can have metameries (http://en.m.wikipedia.org/wiki/Metamerism_(color)), where different physiclaal signals lead to perception of the same color.

Right, although we have been trained otherwise by rainbow diagrams from birth, colors do not map 1:1 to wavelengths, and most of the light we observe is a mixture of wavelengths; we can only sample an intensity from each of three fuzzy bands of the spectra, and the rest is in our heads.