The tricky bit with color is that we don't see frequency along a single band. Rather, there are 3 bands (RGB) that get added together (plus a fourth input for brightness as well as many sub-processes that deal with textures and patterns). Light of a single frequency excites one band a lot, the other a little, and the last almost none. This sum is what we percieve. Some people are missing a band (usually blue or green) causing color blindness. Either way, a rainbow looks continuous but by mixing light there are many ways to generate the same color. It's all a bit dirty.
The other stuff seems to confuse the idea of error, eg you seem to think "quantity + error = quality". But in such cases, error is usually known (and compensated for) turning the equation into the sum of two 'knowns', leading to another 'known'.
