Why many compounds (or complexes) of d-block elements are coloured?

Ans.  D-block elements have electrons in the d-orbital. The d-orbitals split into two groups,t2g(lower energy) and eg(higher energy) in an octahedral complex. When white light falls in the complex compound, the electron of t2g orbital absorbs a certain wavelength from the white light(VIBGYOR) and moves to eg orbital. The remaining part of the light is then transmitted through the solution. In the transmitted spectrum, there is a missing certain wavelength. Therefore the transmitted spectrum is colored and the complex solution becomes colored.