Welcome to the forum Barry This is normal for FBTs to change color depending on their surrounding and temperatures. I just searched up "Iguana light" under google and saw the UV rating of 5.0 thats too much uvb for your frogs, Stick with something much smaller. Here's the Frog forum care sheet on Fire belly toads Frog Forum - Fire-Bellied Toad Care and Breeding - Bombina orientalis and relatives