Quote - Diamonds also show "fire", which is caused by the prism like splitting of light into a rainbow. You can get some of that effect as I did here by setting up a Color Ramp node with some pastel green and red in it and drive that with an Edge_Blend node. I'm showing that in the screen cap above. Thus you see some purple and green in the diamond reflections.

 

Hmm interesting idea, could take a quicker render from that than my way since less raytracing and 1 render instead of 3. But I wonder the difference in end result between the 2, as my way is more of what accually happens, vs a way of "faking it with a painting" so to speak.