I have white playsand, and my Red belly has decent color. 99% of it will be diet and housing conditions, healthy/happy fish = color. Besides the sand I currently have, I've kept rbp on blue gravel, pool filter sand, and hot pink gravel; the pink gave me the best color out of one particular fish, at the time he was 3" or so... But yea, best bet for best color? Good diet, clean water.