I am trying to increase the quality of my diamonds in Keyshot. I'm still getting some dull gray areas in the 'kite' facets. Any tips or tricks in Keyshot I can try?
I'll bet this has to do with your lighting. Test a black and white environment and see if that gives you what you're after.
I agree with Will it's the lighting. if you want to keep the gradient horizon use a plane with a black emissive material (turn off cast shadows and hidden from the camera) as an environment blocker. The pure black should catch in the facets nicely and youll still have the horizon.
Sometimes a scoche of chromatic aberration adds realism.