When I was about twelve years old, I came up with an idea for a massive practical joke to play on an unsuspecting baby. For its entire childhood, everyone around the baby would conspire to convince it that the sky was green. Then at some point in the future, perhaps in front of the entire sixth grade class at Whitworth Elementary School, the truth would be revealed, and one poor kid's world would be turned upside-down.
Somehow I was never able to recruit enough people to pull this ruse off, but it does beg the question: would such a joke even be possible, or would our natural perceptual categories outweigh the influence of hundreds of tricksters? In short, do children understand the differences between colors first, or do they simply learn the names for colors without understanding what they signify? While they were probably not inspired by an idea for a practical joke, Nicola Pitchford and Kathy Mullen of McGill University were able to devise an experiment to begin to address the question ("The Development of Conceptual Colour Categories in Pre-School Children: Influence of Perceptual Categorization," Visual Cognition, 2003).
A large body of research has shown that adults categorize colors into eleven basic categories: white, black, red, green, yellow, blue, brown, purple, pink, orange, and grey. These categories have been tested extensively, even across cultures, and found to be readily identifiable by all adults. When asked to name colors across a wide spectrum of possibilities, most people use the basic color categories to describe even the colors that fall on the border between two categories.
Young children also learn these categories, but only gradually. A very young child might use the same name—say, blue—to describe a wide variety of colors (in fact, two of the 2-year-olds that Pitchford and Mullen studied used "blue" to describe all 11 colors in their study).
Pitchford and Mullen asked kids ranging from age 2 to 5 to name the color of the outfit a cartoon character was wearing. Not surprisingly, the older kids were more accurate, but most interesting was the type of errors the children made. Colors can be arranged in a color wheel (or more accurately, a three-dimensional solid). Some colors, such as orange and yellow, are closer neighbors on the color wheel than others, such as blue and red. The researchers analyzed the errors kids made naming colors and came up with the following result:
Children were sorted by language ability. Those with the ability of an average 2-year-old made the most color errors—but they made an equal number of errors for colors that were distant on the color wheel compared to adjacent colors. It's as if they simply randomly selected a color when they weren't sure about its name. By contrast, the 3-year-old language group, when they made errors, were more likely to pick adjacent colors—saying "yellow" when the color was orange, for example. While the 4-5 group was even more accurate, the few mistakes they made tended to be naming adjacent colors (the distinction between grey and brown is the most difficult, and errors are even made by some adults).
So it seems that toddlers, while able to learn the names of some colors, haven't yet developed an understanding of the relationship between colors. By the time they are three, kids have learned most of the basic colors, but they have also learned more about how the colors relate to each other. Older kids still make some mistakes, but nearly all of them are in related colors, so they're almost always in the ballpark of the correct color.
I suspect this means that my 6th-grade prank would have stopped working long before its victim even entered elementary school. Aspiring pranksters, be warned: better to stick with water balloons and dribble glasses than mess with the human perceptual system.