Ferroxyl contains the chemical compound Potassium ferricyanide which reacts with the ferrous ions to produce the color \"Prussian blue\". Iron is being oxidized at the anode and creating Ferrous (Fe+2) ions. Therefore, with the introduction of Ferroxyl, the anode will turn blue as the Ferroxyl reacts with the Ferrous ions. It is also worth noting that this is a acidic solution and the blue pigment is insoluble in water. This is useful in detecting metal oxidation that leads to rust. Same thing basically for the OH. Solution Ferroxyl contains the chemical compound Potassium ferricyanide which reacts with the ferrous ions to produce the color \"Prussian blue\". Iron is being oxidized at the anode and creating Ferrous (Fe+2) ions. Therefore, with the introduction of Ferroxyl, the anode will turn blue as the Ferroxyl reacts with the Ferrous ions. It is also worth noting that this is a acidic solution and the blue pigment is insoluble in water. This is useful in detecting metal oxidation that leads to rust. Same thing basically for the OH..