Tyrosinase negative amelanism results in your typical albinos. They are white and yellow because they have no tyrosinase present, which means no melanin (black/brown pigment protein) is manufactured. Tyrosinase positive amelanism is a bit different in that a mutation causes tyrosinase to no longer manufacture melanin, but because the tyrosinase enzyme is still present in their skin, it gives them the "caramel" colour.
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