Purple is the meeting of two opposed colors in both physiological and psychological significance. The satisfying calm of blue buffers the penetrating and active force of red.
Thus the stimulus is shown to be ambiguous. Purple can be thought of as a precision scale. And today, you can see this color on the following aesthetic purple wallpapers.
One plate measures the soothing effect of blue on the parasympathetic, and the other plate measures each oscillation of red and its exciting action. Purple shows awareness.