Among $MnS,NiS,CoS,$ and $ZnS$  the total number of BLACK coloured sulphides is :

$M{n}^{2+}$ $MnS$ pale pink $7\times {10}^{-16}$

$Z{n}^{2+}ZnS$ White  $7\times {10}^{-26}$

$C{o}^{2+}CoS$ Black  $7\times {10}^{-27}$

$N{i}^{2+}NiS$ Black  $1.1\times {10}^{-27}$