ocellaris also have less prominent facial features. true percs have a gently sloped nose with lips that kinda poke out more, the ocellaris have a more rounded nose. true percs have more black edging to their stripes while ocellaris have very little. the orange on ocellaris is more like someone colored them with a crayon, it is usually a bright orange, and with age there backs start to turn brownish. true perculas are a deeper darker orange.
i really dont know why it is so hard for people to tell the difference between the two, its not that hard at all to tell you the truth. not to sound rude.