Well, we could of course draw the analogy between colors of the spectrum and tones of sound

Puzzle: We sense colors, which exist on a continuum, by how near one color is to each of the only 3 colors our retinas can sense directly, plus intensity. We sense tones, which exist on a continuum, directly - we can sense each separate wavelength directly. Yet we have the impression that there are more colors than sounds - we draw sounds on a line, but colors in a plane.