Further according to spectrochemical series the strong ligand possessing complex has higher energy and hence lower wavelength. Therefore, complexes containing $N O_{2}, N H_{4}^{+}, O^{2-}$ etc., ligands show yellow colour while $\mathrm{CN}^{-}$ forces the complex to impart white colour.

Spectrochemical series $I^{-} < B r^{-} < S^{2-} < S C N^{-} < C I^{-} < N O_{3}^{-} < N_{3}^{-} < F^{-} < O H^{-}$

$ < C_{2} O_{4}^{2-}=H_{2} O < N C S^{-} < C H_{3} C N < p y < N H_{3} < e n$

$ < b i p y <  phen  < N o_{2}^{-} < p p h_{3} < C N^{-}=C O$