There is a rare genetic trait known as
tetrachromacy,
whose carriers have four colour receptors in their eyes
The carriers are invariably women (because of genetics), and can perceive
colours in ways normal people cannot. It is unknown how many of these
mutants there are walking among us, and it's likely that they themselves
may not even know...
The vast majority of us have no idea what tetrachromacy would be like. Anyone
who had the supersense wouldn't know she did, let alone be able to describe
it. After all, it is an exercise in futility for trichromats to try to explain
their visual experience to color-blind people.