Vanadium oxidation states
Distinctive colors reveal the oxidation states of vanadium (V) in certain aqueous solutions: V+2 (violet), V+3 (green), V+4 (blue) and V+5 (yellow) 

Vanadium oxidation states

Distinctive colors reveal the oxidation states of vanadium (V) in certain aqueous solutions: V+2 (violet), V+3 (green), V+4 (blue) and V+5 (yellow) 

(Source: Flickr / igeldard)