Zn salts are white while Cu2+ salts are coloured. WHY?

Zn has electronic configuration = 3d¹⁰4s²

Zn²⁺ = 3d¹⁰

Cu = 3d⁵4s¹
Cu²⁺ = 3d⁴

In case of Zn fully filled d orbital is present therefore no d-d transition can be possible in this case and it is colorless. 

In case of copper because of d-d transition electrons emits light in the visible range and hence they are colored compounds.