Normally, for a typical fish, the color of the food does not determines the quantity of it that a fish is going to consume. Is either, the fish like the food or not; if it likes the food it will eat it until it is satisfy, if it does not like food, the fish would not eat it.
On the other hand, the effect that the food color may have on the quantity of food a fish will eat may be different under an experimental setup which involve manipulation of different factors which are categorized as dependent and independent factors.