In a group, you can get young dominant males to turn blue early if there are not other more dominant males. Same with Aulonocara.
Other than that, males should color up when sexually mature at 3". Fryeri/Ahli are the best at holding color which is why they are so desirable, they really need to be really stressed to show no color, because the blue male color is part of their hunting camo. Fryeri pretend to be safe breeding Aulonocara to sneak up on prey in nature. Wolf in sheep's clothing type idea.