Is there a correlation with valence electrons and the color of a compound (color vs. white/colorless)?

Question

If so, what is it? And what does this have to do with unpaired valence electrons?

Also, make this applicable to nitrates. I know if it is a main group cation, it will be colorless or white. I know if it is a transition metal, it will be colored. But why? try to answer this by telling me about UNPAIRED VALENCE ELECTRONS

Answer 1

Unpaired valence electrons on organic molecules make something a radical, which is a very reactive type of molecule that you don't see very often (except for molecular oxygen which you breathe all the time).

The reason most metal complexes are colored whereas most organic molecules are not has to do with electronic transitions--most metal ions have unfilled d orbitals, and the electronic excitations involving d orbitals are typically of lower energy (longer wavelength) than those that occur for s and p orbitals (for organic compounds). This is why those transitions occur in the visible spectrum for most metal compounds but in the UV spectrum (invisble to the naked eye) for most organic compounds.