I have golden albino axolotls, and all along their tails you can see what looks like little flakes inside that catch the light. I think what your wild type may have is some of this reflective pigment, which is totally normal and cool if your wild type has some! This would explain the way it changes with light.
The sentence below explains this in detail.
The colour of axolotls is dependent upon pigment cells called chromatophores. These cells are melanophores (containing eumelanin, a black-brown pigment), xanthophores (containing carotenoids and pteridines, yellow and reddish pigments) and iridophores (containing crystalised purines, which impart a shiny iridescence).
I hope this helps and puts your mind at ease!