Setup affecting coloring

So, My baby leucistic axolotls are at the back limb bud stage, for the most part. I have three groups, two in Tupperware, one in a 35 gallon tank with lots of plants. I've noticed two distinct size groups, but these are in no way related to habitat. The bigger ones are all around the same size and have back limb buds, and the smaller ones are the same size as each other without back limbs. I scooped a few out of the big tank and added them to the tupperware group, and noticed something very obvious, and interesting.

The ones in the containers are very pale white, with pink already showing in the gills. Almost no pigment "freckles". The newcomers I moved from the group tank on the other hand are showing a lot of freckling and pigmentation. Any guesses as to the cause of this? Food should be the same, but lighting and temperature are both different. Tupperware is slightly warmer, and more brightly lit.

I have seen this in axolotl larvae and an adult that I raised. In this case its a wild type that generally lives indoors in an aquarium. When she comes for her holiday ( I 'baby' sit her while her owner is on holiday) She lives outside in a large light blue crate, with in a few days she has lightened to the extent her owner was skeptical it was the original axolotl. When she goes back home she darkens again.

That is really neat. So a more brightly lit tank will yield lighter colored axies? or could it be due to substrate color?

Substrate is one way. They will lighten up on a lighter substrate and darken on a dark substrate.