Where is the frog getting pigment(s) other than melanin in this assumption?? Why would the frog be stimulated to deposit a different carotenoid as UV protection when melanin is 1) what is stimulated when exposed to UV light 2) is the pigment used pretty universally in vertebrates to protect from UVB?
It was just an idea man.
I really should clarify, the "deeper red" I honestly meant FROM the formation of melanin (ontop of the supplementation and development of xanthophores), so the frogs take on more of a burgandy, maroon color. What I was wondering, perhaps if the frogs got enough supplementation, and added ultraviolet light, production of xantho and melanophores would give the frogs a deeper shade of red....
But considering you pointed out that xanthophores will be converted to melanophores, perhaps this idea is invalid.