Yeah i love watching my fry develop their colors, a little fry for example that managed to survive right from the start of me moving to my new home just over 3months ago, started off just brown.
1month old his tail color started to turn yellow and the brown coloring concentrated at the base of his tail.
2months old he started to develop large black dots on his tail by which now was strong yellow.
3months old he's started to develop a red edging to his large leopard spot like tail.
He's very gorgeous and im positive he's going to grow to a large size, he's already almost the size of a muture male guppy at only 3months old and very active- he was a surviver of the "survival of the fittest" technique of raising fry and im looking forward to the offspring he'll produce if he gets some female attention away from the other 3 guppy males in the tank .
Good luck with raising your fry, im sure they'll turn out healthy and beautiful if you care for them well !