Why hydrated CuSO4 is blue while anhydrous CuSO4 is white??

The correct answer is - water acts as a ligand that splits d orbitals.

Explanation:

Hydrated CuSO4 has a central metal (Cu) surrounded by the water molecules, here water molecules play a role of the ligands that causes the splitting of d-orbitals. This splitting brings d-d transition and emits the blue color of Cu in the visible light.

Anhydrous CuSO4 on other hand is colorless due to the lack of molecules of ligand that makes splitting of d orbitals impossible so no transition of d-d orbitals takes place and no emission of color.