Corinne and Elissa gave you such great answers, that I really have nothing to add!!!
I will only say that definately seek out a Vascular Abnormalities specialist for a correct diagnosis. It is very important to get a correct diagnosis for many reasons, but I will name a few.
If it is on or near his eye, you have to see an eye doctor for evaluations -to rule out any possible eye issues.
It is is on T-1 and or T2-these areas which include the upper and lower eyelid, temple,forehead, upper cheek- you would need to rule out SWS.
ANd yes, there are Doctors who will laser an infant. We began laser tx on my daughter when she was six weeks old. If it is a pws, laser is done for cosmetic BUT medical issues is the main reason. They can have future medical issues later on in life.
ALso, hot and cold tend to affect PWS. When my daughter is sleeping, you can barely see the outline. But you put her in a pool, or if she gets mad, it looks very dark. It changes with her mood. If she is sick, or with fever, it gets darker. I know before she shows symptoms of illness that she is getting sick because her pws gets so dark. Other people say that it lightens with heat and is darker in cold. Every pws is different.
Hang in there and do not stop searching for a correct diagnosis for your little one. There is nothing wrong with getting a second, third and fourth opinion if needed.
Please keep us posted. And ask any questions that you may have.