Oxy-hemoglobin, i.e. that which has coordinatively bound oxygen, is red in colour and this gives the see-through body of daphnia a red pigmentation. Individuals of the same strain in oxygen-rich environments tend to be yellow or almost unpigmented. An example of a species that seems to exist with very little hemoglobin in comparison to other members of its genus, is Daphnia hyalina. It is usually found in the open water of lakes where dissolved oxygen is plentiful. The colour is also moderated by what food is predominating in the diet. Daphnia fed on green algae will be transparent-green in colour, while those feeding on bacteria will be salmon-pink. Taken off http://www.caudata.org/daphnia/