A pink coloured salt turns blue on heating. The presence of which cation is most likely?

Due to the presence of  ${\mathrm{Co}}^{2+}$ cation pink-coloured salt turns blue on heating.

When heated, the blue salt, which is hydrated copper sulphate  $\left({\mathrm{CuSO}}_4\cdot 5{\mathrm{H}}_2\mathrm{O}\right)$ loses its water of crystallisation and turns into white anhydrous copper sulphate ${\mathrm{CuSO}}_4$. The anhydrous form rehydrates and regains its blue colour when water is added.