Here is a very detailed examination on how pigmentation in the cuticle of a butterfly wing scale changes the density and refractive index of chitin and, thus, also alters structural color. rdcu.be/eyUwS

For those interested in the evolution of phenotypic plasticity - Shen Tian et al. found that a novel bit of DNA - a Hox gene promoter in the genome of satyrid butterflies - boosts plasticity in the size of their eyespots in response to temperature.
www.biorxiv.org/content/10.1...