In the interest of totally unnecessary and actually rather gross headcanons, part of the reason Charles has such an affinity for iguanas is because he feels a connection to them when it comes to the shedding of skin. 

Generally speaking, Charles gets a wickedly rough sunburn when the weather returns to the searing heats he is used to – and after a bit is capable of peeling his skin in relatively large strips to reveal new and comfortably tanned skin beneath. It’s disgusting – but the person who hates this most is Jack, seeing as he’s the one who has to strip off the back. 

This tan will hold Charles and he will steadily grow darker as the summer progresses. He likely only has to peel once or twice more throughout the hot months depending on how much exposure he gets on scorching days, with his tan deepening each time, leaving him a fairly nut brown by the end of autumn.