Copper sulfate itself is white/colorless when anhydrous. However, it's hygroscopic and the pentahydrate (the usual form) is blue... in fact, it's just about the same color as the sidebar over to the...
Initial chemical formula is: CuSO4.5H2O. Dehydration: - CuSO4.3H2O at 63 0C - CuSO4.H2O at 109 0C - CuSO4 at 200 0C Thermal decomposition after 650 0C: CuSO4 = CuO + SO3