I'm not sure that the 50/50 or 75/25 thing really applies to pinto or appy? If you breed a solid to a pinto, the offspring is either pinto or solid--if solid, is there pinto "hiding" there behind a few white hairs somewhere, or is the horse a true solid, as in it didn't inherit the pinto gene from its pinto parent? Even though the horse has a pinto parent, if it didn't inherit the pinto gene then you wouldn't say that the horse is half pinto, because in reality he doesn't have a pinto gene.
If you breed a bay Morgan to a chestnut Arabian you end up with a horse that is half Morgan, half Arabian--but he's not generally referred to as 'half bay' no matter what color he is.