aw she's thinks that sherrie is a toreador and she is just playing along!

seriously though, red can be a color that signals aggression or a mating call of sorts. with anoles, the males have a red dewlap that they display either to attract a mate or to warn other males. i'm not totally familiar with how that all works with iguanas but i'd bet something similar is going on and the iguana may associate the red with a male iguana or an aggressor.