Zn salts, such as zinc sulfate or zinc chloride, are generally colorless due to the electronic configuration of the zinc ion (Zn2+). Unlike transition metals that often exhibit vibrant colors due to d-d electron transitions, zinc does not have any unpaired d electrons when it is in its +2 oxidation state.
The electronic configuration of Zn is [Ar] 3d10 4s2. When it loses two electrons to form the Zn2+ ion, it achieves a stable electronic configuration of [Ar] 3d10. In this fully filled d-subshell, there are no available energy levels for electrons to transition between, which is typically required for the absorption of visible light and the resulting coloration.
Furthermore, the ligands surrounding zinc ions in zinc salts typically do not promote any transitions that would lead to color. As a result, these compounds remain colorless, making them quite distinct from many other metal salts that are often vivid and colorful.