I was under the impression that tyrosine deficiency is caused by an excess of the enzyme tyrosinase which breaks down tyrosine - which in turn results in the production of melanin (which woudl explain the darkening).

Tyrosinase is a copper-containing enzyme. So I would guess that an excess of tyrosinase would create a darker animal and a deficiency of tyrosine...........but since the enzyme contains copper, would the animal necessarily be copper deficient?

I would think that copper deficiency would result in anemia and other ailments but I'm probably wrong........

That's the best I can do.........dunno if it helps you..........