Internet assertion:

Humans see colour with red, green, and blue cone cells, named for the colours they best detect.

Human cone peak sensitivities:

Three circles in a row against a dark background, coloured greenish yellow, green, and purple.
566 nm, 541 nm, 441 nm respectively.

This is part of the reason why the labels L, M, and S (for “long”, “medium”, and “short”) are used exclusively in the literature: the traditional names for cone cells have almost no bearing on their actual receptivities.

The other part is to do with how each responds to a much broader range than a single peak, ranges that overlap so no receptor monopolises any of the interior region.