A similar reversible reaction takes place between anhydrous cobalt(II) chloride (which is blue) and water to produce hydrated cobalt(II) chloride (which is pink). Heating pink hydrated cobalt(II ...

Cobalt chloride in fact. However, as far as colours go, cobalt has a few more strings to its bow than just this wonderful blue. Cobalt can also colour glass green, while the hydrated form of cobalt ...