Amongst, ${\mathrm{NiCl}}_4^{2-},{\mathrm{Cu}}_2{\mathrm{Cl}}_2,{\mathrm{ScF}}_6^{3-}\text{ and }{\mathrm{CoF}}_6^{3-}$, the coloured species are

$\text{ (i) }\mathrm{Sc}(\mathrm{Z}=21),3{\mathrm{d}}^{1}4{\mathrm{s}}^2$

${\mathrm{Sc}}^{+3}=3{\mathrm{d}}^{0}4{\mathrm{s}}^0\Rightarrow \text{ Colourless }$

$\text{ (ii) }\mathrm{Co}(\mathrm{Z}=24),3{\mathrm{d}}^{5}4{\mathrm{s}}^2$

${\mathrm{Co}}^{+3}=3{\mathrm{d}}^{4}4{\mathrm{s}}^0\Rightarrow \text{ Coloured }$

$\text{ (iii) }\mathrm{Ni}(\mathrm{Z}=28),3{\mathrm{d}}^{6}4{\mathrm{s}}^2$

${\mathrm{Ni}}^{+2}=3{\mathrm{d}}^{6}4{\mathrm{s}}^0\Rightarrow \text{ Colouress }$

$\text{ (iv) }\mathrm{Cu}(\mathrm{Z}=29),3{\mathrm{d}}^{10}4{\mathrm{s}}^1$

${\mathrm{Cu}}^{+1}=3{\mathrm{d}}^{10}4{\mathrm{s}}^0\Rightarrow \text{ Colourless }$

Formation of coloured compound is due to excitation of e^-'s from  orbitals ${\mathrm{t}}_{2\mathrm{g}} \mathrm{to} {\mathrm{e}}_{\mathrm{g}} \mathrm{orbitals}.$