Hey yes I am looking for an answer to a question.
I have been noticing my son has been having moment when his skin gos blochy what could it be?
It looks like his vains are poping out and get really red.

I don't know what that is. It looks like it could be a localized allergic reaction. Is there a commonality to these attacks? IE, he puts on a t-shirt that GrandMa washed using a different detergent, or different soap, or a certain place? That is where I would start, try to narrow down what is causing this. Of course I would take him to see his doctor as well. Some simple like this could indicate a far worse condition.