What determines the colour of chromium compounds?

[24forChromium]

I am aware of the processes through which cations are coloured in ligand complex (splitting of incomplete d-shell will absorb specific frequencies of the spectrum). However, I am only aware of this interaction with aqueous mono-atomic cations, which is not always a present condition when colours are present in substances.

I am interested specifically in chromium and its compounds' colours, I would like some explanation in terms of interaction with photon and atomic orbitals for the various colours chromium has, and ultimately to narrow done the exclusive causes responsible for chromium's compounds' colours.

I currently believe that the colour of chromium is only dependent on the separation of its d-orbital and unrelated to any other present elements, other elements only serve to modify its d-orbital but does not interact with photons meaningfully themselves.

 

[PietKuip]

Rubies are red. http://www.webexhibits.org/causesofcolor/6AA.html
Emeralds are green: http://www.webexhibits.org/causesofcolor/6AB.html

 

[DrDu]

Just some remarks:
- Ligand field theory is also applicable in solids.
- While ligand field theory explains quite well the wavelength at which d-d transitions occur, these are often not the most intense absorptions present in a compound, as they are dipole forbidden. Rather, in many complexes, the colour seen is mostly due to charge transfer transitions from the ligand to the metal.