Ash's skin color is a mix of Liko's and Roy's skin color. In the first episode of Pokemon, there is a very short scene of Ash's father battling at the Pokemon league and he has skin color like a little lighter than Roy's. If he were to breed with Ash's mother then the biology would make perfect sense. Liko and Roy are Ash's fathers parents.

It also makes sense because it is heavily suggested in the game and the anime that Scarlet/Violet is a prequel to all the other pokemon games and regions.