The other day, I listened to an interesting radio show discussing color and how we "see" it -- or not. Perhaps you didn't know that specialized cells in our eyes, called "cones", are responsible for our ability to see color. We have about 6 million of these cones in each of our retinas. Most humans (and primates) have three types of cones -- ones that allow us to see the blue, red and green range of colors in the color spectrum. Scientists have found (don't ask me how!) that some sea creatures (I've forgotten which and am too lazy to look it up) have many, many more of these photoreceptor cells and their rainbow is way more extravagantly colored than ours.
If a person is "color blind," he or she (but usually a he) is missing one or more of these types of cones. The most common form of color blindness in humans is red/green, meaning the person sees red or green as shades of gray (or possibly some limited shades of red or green.)
Many people think dogs can't see colors at all -- that they are truly color "blind." But, it turns out they can see colors, but because their eyes lack red cones, the same part of the color spectrum that we see as a "rainbow" they see very differently. According to research done by a scientist from UC Santa Barbara, "Instead of seeing the rainbow as violet, blue, blue-green, green, yellow, orange and red, dogs would see it as dark blue, light blue, gray, light yellow, darker yellow (sort of brown), and very dark gray. In other words, dogs see the colors of the world as basically yellow, blue and gray. They see the colors green, yellow and orange as yellowish, and they see violet and blue as blue. Blue-green is seen as a gray." If you go to this site (source of the previous quote) you can see what the color spectrum looks like to people and dogs. Go ahead; I'll wait.
Hi, again. That was interesting, wasn't it?
If you read to the end of the article, you noticed that the author mentioned how odd it is that so many dog toys (including the ever-popular stuffable "Kong") are RED -- a color that dogs can't "see."
Maybe color is the reason Darby and Pumpkin are loving their new BLUE Wubba and YELLOW football toys so darned much -- they aren't just shades of gray!