under different light/angle the fish will have a different hue, I have see anything from a little bit of green speckles, silver speckles to full on blue/purple from the same fish, it doesn't really make the fish more rare but to the potential buyer it may sound more attractive thus can possibly sold for more money.
I personally don't like to feed them pellets, a natural food diet is a better option IMO. feed them fish, smelt, shrimp, etc. mix things up, don't always feed filet only, you would want to mix up with small whole fish (smelt, silverside, etc) to balance out the nutrients.
if you do decide to feed pellets, or add pellets into the food (by stuff it into fish or shrimp, etc) make sure you don't over feed.