It's all about light and camera angle. Personally, I don't like fixed camera stands, I take all my pictures free-hand. I'm far from an expert but I can bring out colors easily. All pictures taken without ANY post-processing (other than to resize). Just different angles:
Good advice. The more vertical you can get the lighting angle the better the color. Lights high and tight to the camera. Axial lighting, which is essentially a pane of glass that redirects lighting to be perfectly vertical (the ideal) does not work with slabbed coins because the plastic creates glare. Experiment with raw coins but don't waste your time with holdered ones. Lance.