Which of the following pairs of ions are colourless?

${\mathrm{Sc}}^{3+},{\mathrm{Zn}}^{2+}$ are colourless because their valence shells do not contain any unpaired electrons. The remaining ions are all coloured because their valence electrons are unpaired.

Hence, the correct option (B).  ${\mathrm{Sc}}^{3+},{\mathrm{Zn}}^{2+}$