I think it depends what fish you have, marine fish would think white sand is natural, Amazonian fish might think black sand is more natural and finally fish from regions I'm not sure of, would think sunset gold was natural although Im not so sure if that one is man made or not. I personally like the look of white sand because it makes the tank much more serene and lightens up the fish but if you have dramatic colored fish black substrate is better. I'm not sure right now what I would do I'm making it a peacock tank so white may be better because the fish will glow but I have seen tanks with black sand that are just amazing