Oxidation test. Two test tubes with two different colours indicating a change in an oxidation state. The oxidising agent used is potassium permanganate and changes from purple (oxidation state: +7) to a green colour (oxidation state: +6). This is due to a reduction (decrease in oxidation state) of the manganese in the manganate ion. This colour change is used to confirm that an oxidation reaction has taken place. In this case, cyclohexene has been oxidised by the potassium permanganate, forming an alcohol: cis-1,2-cyclohexanediol.