i have heard that if you feed them to much repile food (the red stuff you can buy) it can affect the colour of them, but i dont think it does imo.
pandora loves strawberries and she is very yellow not red.and sidney loves pes and shes not green.
ours get a good mix of foods so it hard to tell if the food accects there colours.
ours only change in the heat, like today there colours are amazing, they are so bright.