Click the control or press E to activate.
The Rainbow Phase control, part of the Secondary Diffraction Spikes control group, shifts the colors of the multicolored 'rainbow' pattern in the Secondary Spike effects inward or outward.
Higher Secondary Spike Rainbow Phase values shift the colors outward.
Tip: This control can be handy if you are editing an image with existing diffraction spikes since it will allow you to adjust the 'rainbow' pattern to precisely match an existing 'rainbow' pattern.