Bangaii Carinal grey instead of white

[LeanneP]

My cardinal is looking very grey on his body and his head is more white. I think that he has changed colour and used to be whiter. Does anyone know if this means he is lacking something or is this normal. I feed him mysis shrimp and spirulina brine shrimp. Am I missing something in feeding him? I tried flake food for my fish and they didn't seem to be interested in it.