In hydrated CuSO4, the water molecules surrounding the Central Metal (Cu) act as ligands, resulting in a d-d transition and, therefore, emitting a blue color in the visible region, due to which hydrated CuSO4 appears blue.

?+2 Charge. The proper name for CuSO4 is copper(II) sulphate - the Roman numerals denote the oxidation state for any atom which has variable oxidation states, such as transition metals.

Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula CuSO4.