The colour of ${\mathrm{Sc}}^{3+}$ compounds would be

The configuration of ${\mathrm{Sc}}^{3+}$ is $\left(3\mathrm{s}{)}^2\right(3\mathrm{p}{)}^2$2 and thus there is no electron in the 3d orbitals and hence no electronic transition within 3d orbitals can take place.