The blue colour is due to the water of crystallization (CuSO4.5H2O). When this is removed by heating, basic copper sulphate is left (CuSO4.H2O) and this can be further broken to simple CuSO4. It is essential you realise the water is not there as free liquid, but as a molecule in its own right and it is bound to the copper atom. These molecules fulfill a structural role in as much as they fill voids in the crystal structure and let the salt ions take up a regular and therefore crystalline, shape of minimal energy content. In the case of all transition metals, the water of hydration is linked to the d (or higher) orbitals and these distort slightly, thereby causing a band energy shift that is characterised by the colour. In the case of copper this shift is in the 600-900 nm region and this is where the blue-green colours occur. The envelopes of these bands are generally unsymmetrical and encompass several overlapping transitions !!! hOpe iT wILL heLP ... cHeeRS
) which causes the splitting of it's d orbitals and thus d-d transition takes place and due to which 
is blue in color.