The blue colour of $$CuSO_{4}$$ solution is due to the presence of $$Cu^{2+}$$ ions. The change in intensity of the colour of $$CuSO_{4}$$ solution because when the $$Zn$$ rod is dipped in $$CuSO_{4}$$ solution, the $$Cu^{2+}$$ ions in the solution get, deposited at the $$Zn$$ rod as $$Cu$$ atoms.