I've heard that due to some mutation certain people can see a wider range of colors (within the same spectrum). I think the general idea is that instead of seeing 7 colors in a rainbow they see 10, or something along those lines.

I don't remember exactly where I heard this, but is it true? And if so, how does it work?

I was also under the impression that color sensation in human beings is a bit "sloppy." That the way our nervous system responds to different wavelengths of light isn't always accurate or evenly distributed.