Why hydrated copper sulphate is blue while anhydrous copper sulphate is white?

Explanation

In hydrated copper sulphate, four water molecules are present as ligands. In the presence of these ligands, the d-orbitals split up into different levels and hence these are no longer degenerate. Hence, d-d transitions take place absorbing red wavelength and complementary blue colour is reflected. On the other hand, in anhydrous `CuSO_4`, d-orbitals remain degenerate because of the absence of ligands. Hence, no d-d transitions can occur and the anhydrous `CuSO_4` is white.