The Riffins are a great family aren't they? Chantrelle is my favourite too!
I wonder if, before they died, one of Calvin's parents has pink hair? I'll check the wiki.
EDIT: The Wiki has confirmed my suspicions. Because they died in a fire, Clarissa and her husband Clement both show up with pinkish skin and hair, I think even when revived with Ambrosia. So that's where your heir got the hair colour.