you bought the right one the slender rainbow style ones are just starved to keep the lfs tanks clean ,they fatten up nicely & wont scratch you with anything when hand feeding a mounth or 2 after purchase. as for colour a blacker oe is nicer,I find it deep ends :dive2: :dive2: :dive2: on what you feed them . they are gold probably from shrimp pellets or algae waffer discs. I cant imagine what food is gold anyhow my black shark is now about 18 inches & turns red when fed live blood worms grey with the center of scales (wich are as big as alot of the fish in the tank) deep red. he also turns grey & blackish @ times but I dont have any black worms .sometimes when I go away he gets desperate & eats someone small when I find him some strange colours lol . hes ainly a big softy & is very resposive to us .The only drawback is hes not a day person.<Ours is a big fatty because he knows how to get our attention allowing him 2 b fed twice ussualy but if he misses it the shrimp or loaches dog out his scraps. Ide say one of our coolest features though we dont hand feed him he has a cave he hangs out in when hes out with his fins all spread its magnificent 9the only living thing that can enter a hipopotomuses mouth is the freshwater black shark ! <><