Explain the origin of colour in coordination compounds.

(N/A) When white light passes through a coordination compound,a portion of the visible spectrum is absorbed. The light that emerges is no longer white; its colour is the complementary colour of the light that was absorbed.
The complementary colour is generated from the remaining wavelengths of the visible spectrum.
For example,if a sample absorbs green light,it appears red. This phenomenon can be explained using Crystal Field Theory $(CFT)$.
Consider the complex $[Ti(H_{2}O)_{6}]^{3+}$,which is violet in colour. This complex has a $d^{1}$ configuration. The single electron occupies the $t_{2g}$ level in the ground state. Upon absorbing light,this electron undergoes a $d-d$ transition to the higher energy $e_{g}$ orbital. The energy of the absorbed photon corresponds to the crystal field splitting energy $(\Delta_{o})$,which falls within the visible region.