The Colour of KMnO₄ is due to 

• M → L charge transfer transition

• d-d transition

• L →M charge transfer transition

• σ →σ*

C.

L →M charge transfer transition

KMnO₄ → K⁺ + MnO^-₄
Therefore,
In MnO₄^-, Mn has +7 oxidation state having no electron in d- orbitals.
It is considered that higher the oxidation state of metal, greater is the tendency to occur L →M charge transfer because ligand is able to donate the electrons into the vacant d- orbital of metal.
Since, charge transfer is Laporte as well as spin allowed, therefore, it shows colour.