As you know, melanism occurs with varying degrees among yellow anacondas, I have a breeding pair, the male is reduced melanism and the female is quite dark. The litters I have produced are all born quite dark, and after the first couple of sheds start to show which ones will lighten as they get older, a couple will be quite reduced, a couple dark, and the majority somewhere in the middle. I believe though they could be line bred to be high contrast or very reduced melanism.
Mike