How do I turn down the saturation of a specific color in the noise texture? I am using the noise texture to fake the dispersion in a glass shadow. It looks cool, but there is a problem, the noise texture has the purple color, while the purple color is not one of the rainbow colors. How do I get rid of the purple color in the noise texture?

EDIT: I am not sure about whether the rainbow has purple or not, maybe it has. But I would still like to know how to twick a specific color in noise texture. I tried using the Hue/Saturation node and it did not work.
You can put the FAC out of the noise texture into a color ramp, which lets you choose your own color for every range of value (between 0.0 and 1.0) of the texture.