The colour of the copper layer deposited on a graphite electrode during electrolysis of an aqueous solution of copper(II) sulfate looks whitish-grey when inspected in situ. Taking the electrode out of the solution reveals the familiar orange-red colour of deposited copper. The explanation is found in terms of the almost ideal complementary colours of the copper metal (orange red) and the copper(II) sulfate solution (bluish-cyan). Electrolysis can be defined as a process of chemical change occurring on the electrodes in a solution (or in a melt) as a result of a direct current between the electrodes. The changes are simply the reactions of reduction (on the cathode, the negatively charged electrode) and oxidation (on the anode, the positively charged electrode). Examples of electrolysis may be found in Fowles (1959), Roesky and Mockel (1996), Shakhashiri (1992), and Summerlin, Borgford, and Ealy (1987). Many more can be found on the World Wide Web. One of the most familiar, and also least expensive, demonstrations of this phenomenon is the electrolysis of an aqueous solution of copper(II) sulfate. Simply place two graphite electrodes in a solution of, say, 1 mol/L CuSO[subscript 4](aq), connect the electrodes to the poles of a source of direct current (approximately equal to 5-15 V), and inspect the electrodes after several minutes. The electrode connected to the negative pole (the cathode) is covered with a layer of elemental copper that can be recognized by its characteristic orange-red colour. No visible changes to the anode are detected. One of us (VMP) has performed this demonstration dozens of times over several decades. However, if it was not for students recently noticing something odd, the phenomenon being reported and analysed here would have probably remained unnoticed. (Contains 1 note and 4 figures.)