Why is cadmium carbonate colorless?

Answer 1

The 'd' orbitals of Cadmium are full filled therefore transition of electrons is not possible within 'd' orbitals so compound is colorless.

Answer 2

Cadmium carbonate is colorless because it does not have any d-orbital electrons which could lead to d-d transitions responsible for color in transition metal compounds like in cadmium sulfide. The absence of these electrons means that cadmium carbonate does not absorb visible light and therefore appears colorless to our eyes.