What Fogey said...why would they? Fish can color up, but just b/c they can, doesn't mean they will. They usually color up to exert dominance or earn the attention of a mate. I have some males (all male tank) that colored up nicely and others that refuse to. I normally get the best colors when I purchase them mostly mature and colored up. They don't tend to develop the same colors unless they got them elsewhere. Once they get them, they don't really lose any color.