Why are complex ions containing transition elements coloured?

Firstly a transition element is an element which forms one or more stable ions with incompletely filled d orbitals.Ligands are charged or neutral, ions or molecules, which form coordination bonds with a central metal ion to form a complex. When ligands are bonded to a central transition metal ion, the d-orbital is split into two sets.One set is at a higher energy level than the other.Because this is a transition metal, the split d-orbital is not completely filled.Therefore there is space for an electron to transition to the higher energy level. The complex will absorb certain wavelengths from the visible region of the spectrum.The energy absorbed from photons of these wavelengths provides the energy for an electron to be promoted. The colour we see, is the wavelengths of white light that are not absorbed by the complex.