I'll be the first to admit that i'm not a Doctor or all *that* knowledgeable about birthmarks, but I've always thought that stork bites were a type of PWS...
I've got a PWS on the left side of my forehead & my left eyelid. It turns redder when hot & even purple/pink if i get really cold, similar to how yours does.
Have you noticed if its getting cobble-stony or thicker or anything?
The hope a dream and the wings to be free