$$L \to M$$ charge transfer spectra. $$KMn{O_4}$$ is colored because it absorbs light in the visible range of electromagnetic radiation. The permanganate ion is the source of color, as a ligand to metal, $$\left( {L \to M} \right)$$ charge transfer takes place between oxygen's $$p$$ orbitals and the empty $$d$$-orbitals on the metal. This charge transfer takes place when a photon of light is absorbed, which leads to the purple color of the compound.