ionic compounds - Why is MnSO4 colourless?

I get it that transition metal salts have colour due to d-d transition from $\mathrm{t_{2g}}$ to $\mathrm{e_g}$ orbitals in octahedral and the opposite in tetrahedral but why would $\ce{Mn^2+}$ not have any characteristic colour? Is it so because the orbitals are degenerate in $\ce{MnSO4}$? or because d-d transition only takes place when there is completely empty d orbital?