When you bring home the wrong color of paint from the hardware store, it may not be your foggy memory at fault. A new study finds that while the human brain can distinguish between millions of colors, it has difficulty remembering specific shades. 

For example, most people can easily tell the difference between azure, navy and ultramarine, but when it comes to remembering these shades, people tend to label them all as blue, the study found. This tendency to lump colors together could explain why it's so hard to match the color of house paint based on memory alone, the researchers said. [Eye Tricks: Gallery of Visual Illusions]

Many cultures have the same color words or categories, said Jonathan Flombaum, a cognitive psychologist at Johns Hopkins University in Baltimore. "But at the same time, there's a lot of debate around the role those categories play in the perception of color," he said.

In the study, Flombaum and his colleagues conducted four experiments on four different groups of people. In the first experiment, they asked people to look at a color wheel with 180 different hues, and asked them to find the best name for each color. The exercise was designed to find the perceived boundaries between colors, the researchers said. In a second experiment, the scientists showed different people the same colors, but this time they asked them to find the "best example" of a particular color.

For a third experiment, the researchers showed participants colored squares, and asked them to select the best match on the color wheel. In a fourth experiment, another group of participants completed the same task, but there was a delay of 90 milliseconds between when each color square was displayed and when they were asked to select the best match on the color wheel.

The results revealed that categories are indeed important in how people identify and remember colors. The participants who were asked to name the colors reliably saw five hues: blue, yellow, pink, purple and green. Most of the colors were given one name, butambiguous colors got two labels, such as blue and green. "Where that fuzzy naming happened, those are the boundaries" between colors, Flombaum told Live Science. In addition, people tended to choose the same shades as the best example of each color.

But what was really striking was how the people in the memory experiment remembered the colors they saw, the scientists said.

The researchers expected that the participants' responses for what colors they had seen would reflect a bell curve centered on the correct color. But instead, they found that the distribution of responses was skewed toward the "best example" of the color they had seen, not the true color.

The findings suggest that the brain remembers colors as discrete categories as well as a continuum of shades, and combines these representations to produce a memory. There could be many reasons for this, but it likely boils down to efficiency, Flombaum said. "Most of the time, what we care about is the category," he said.

And this tendency to store memories in categories extends to other things besides color vision. "In general, we tend to remember things as more similar to our expectations of how those things are," Flombaum said.

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