I have been warned by some of my suppliers to be careful about where you get your cultured clams. They claim that some clam farmers breed their clams in tanks and then move them to raceways in the ocean to grow them out. When they are large enough to sell, they go collect them out back out of the ocean. The main problem with this method is that they are susceptible to getting diseases and parasites while in the ocean. A true cultured or farm raised clam is never put in the ocean...it spends it's entire life in a tank.
I think the reason wild caughts have better color has to do with gene diversity. There are more parent clams in the ocean exchanging gametes than in clam farms. I don't know that much about genetics, but it seems that farm raised clams are kind of "inbred".