I think he is talking about optical illusions like the "Checker Shadow Illusion": http://www.businessballs.com/shadow-optical-illusion.htm http://www.businessb

I think he is talking about optical illusions like the "Checker Shadow Illusion": http://www.businessballs.com/shadow-optical-illusion.htm http://www.businessballs.com/shadow-optical-illusion.htm So we perceive the same color as a different one depending on the other colors surrounding it (also http://www.designmatrix.com/pl/cyberpl/cic.html http://www.designmatrix.com/pl/cyberpl/cic.html ) I'm not sure there is any art training that can change your brain to make this illusion not work. Using a tool like the mirror device in the article, makes it easier to match colors because it can remove the other colors around it and also moves it closer to the color you are painting.