Why purple seems so to similar to red?

Question

Purple lights has the highest frequency among all visible lights, while the red lights is the least frequent one. However, purple seems to be a mix of red and blue to human eyes, why?

Answer 1

There are three pigments in the human eye cone cells and combinations of their light sensitivities are the basis of our color vision. These pigments are red, green, and blue. The violet end of the spectrum excites blue pigment only. Less-extreme 'blue' perception includes some slight green pigment response.

The color that results from red and blue pigments excited, but no green, is called 'magenta'.

So, the color we call 'purple' can be violet (all blue) or blue-plus-red, hopefully with not much red (that would merge from purple to magenta). On a color 'wheel' diagram, the purple area is mainly-blue, but away from the green border and toward the magenta (which is equal blue+red).