I do know that other changes, especially being ill, can affect the way a hemangioma looks. I mean color changes are normal if the child cries or gets upset or if there is a change in temperature.
Has he had any imaging studies done? ultrasound? mri?
What does it look like this morning (it's Monday here)?
Is there anything you can think of that might have been different this weekend? Did his grandmother give him any medication (like a fever reducer ... advil, tylenol, etc) or could she have fed him a food he'd never eaten before?
Can you post a photo? If you have one and can't post it for some reason (a lot of cameras, even phone cameras, take pics that are too large to post) send it to me at firstname.lastname@example.org
and I'll post it for you.
Ask an expert if you'd like: I'd suggest Dr. Levitin http://birthmark.org/node/152
Call his doctor as soon as you can.