Why are different colours observed in octahedral and tetrahedral complexes for the same metal and same ligands?

(N/A) The colour of coordination complexes arises from $d-d$ transitions,which depend on the magnitude of crystal field splitting $(\Delta)$.
For the same metal ion and the same ligands,the crystal field splitting energy in an octahedral complex $(\Delta_o)$ is significantly larger than in a tetrahedral complex $(\Delta_t)$.
The relationship between them is given by $\Delta_t = \frac{4}{9} \Delta_o$.
Since the energy gap $(\Delta)$ is different,the wavelength of light absorbed $(\Delta E = \frac{hc}{\lambda})$ is different,leading to the observation of different complementary colours for the same metal-ligand system.