In terms of physiology, the color is stimulated in the brain when the eye reports input from short wave blue cone cells along with a sub-sensitivity of the long wave cones which respond secondarily to that same deep blue color, but with little or no input from the middle wave cones. The brain interprets that combination as some hue of magenta or purple, depending on the relative strengths of the cone responses.
In terms of physiology the color is stimulated in the brain when the eye reports input from short wave blue cone cells along with a sub,-sensitivity of the long wave cones which respond secondarily to that same deep blue color but with little or no input from the m,iddle wave cones. The brain interprets that combination as some hue of magenta or purple, depending on the relative strengths of the cone responses.