Dogs are "colorblind" but that word might not mean what you think it means. There are different kinds of colorblindness and with most kinds, you can still see some color. Dogs see the difference between yellow and blue clearly. That's why Cooper is only sorting yellow and blue at the moment. I may be able to add in one or two more colors if the shades are different enough for him to tell them apart, but color-wise he will only ever see a big difference between blue and yellow. You can learn more about how dogs see color at http://dog-vision.com (not my website, but very helpful). The images below - taken from dog-vision.com - show a full RGB color spectrum and how the same spectrum would be seen by a dog:
Human's view: Dog's view:
I didn't exactly "train" him to recognize color. I trained him to put the cotton reels in the right bowl based on their color. I doubt that he is truly recognizing the colors or sorting by color. He is able to do it correctly most of the time, but not all of the time. It's more than luck, but he doesn't seem to fully understand what he's doing either and he might not ever fully understand. I am testing the limits of his intelligence, so there are certain tricks he might not ever be able to perform correctly 90-100% of the time. The color sorting is one of those tricks.