Do you have a full body picture of him? It may be an appaloosa pattern on top of a pinto pattern that is causing him to be predominantly white. Varnish roan can cause a horse to look almost completely white while still maintaining the dark skin underneath.
A 'solid' Paint refers to a Paint horse that comes out completely solid colored (bay, chestnut, palomino, etc - aside from face/leg white which is still caused by pinto genes). So technically your horse isn't solid so much as he's ridiculously loud/maximum expression of pattern. There are a few reasons your boy can have the mismatch of black and pink skin. The biggest one would be if he is grey and his color just faded out, the black skin would still be there but the hair would turn white over time. Since you say you got him young, how young are we talking? Young enough for a grey to not be fully white?
I honestly can't really think of any other reason a completely "white" Paint horse would have both black and pink skin all over his body. (as a reference, there's an 11yo completely "white" grey stallion at the farm Reno is at, and his colt is just over yearling and is well into greying)