In my opinion sand is the best way to go, the play ground sand at home depot is awesome, its lighter colored, but gives the tank a lot more natural look. The color of the substrate does bring out some colors on fish better, but a better effect I think is to dull the lighting, becareful of doing this with plants though as some may not get enough light, and if your doing it with planted tanks, let the plants diffuse the lights for you. Brings out the colors great.