Always factors...lighting, anem or no anem, feeding, etc. With B&W ocellaris, it has been determined that by about age 3 they will be completely black and white, but with onyx percs it is much more widely varied. Perculas do not fully develop until a later age and you can see black coming in for years. Then again, it will be mostly hypermelanized in the first couple years to few years. That does not meant that is when you'll see color starting. Once settled, it should start coloring up fairly shortly and continue to fill in over time. I know it is not a great answer, but I hope this helps.