In cognitive realms, experts say colors may affect performance because of the mood they transmit.

"When things go wrong or when you feel that the situation you are in is problematic, you are more likely to pay attention to detail, which helps you with processing tasks but interferes with creative types of things," said Norbert Schwarz, a psychology professor at the University of Michigan. By contrast, "people in a happy mood are more creative and less analytic."

Many people link red to problematic things, like emergencies or mistakes on tests, experts say. Such "associations to red - stop, fire, alarm, warning - can be activated without a person's awareness, and then influence what they are thinking about or doing," said John Bargh, a psychology professor at Yale. "Blue seems a weaker effect than red, but blue skies, blue water are calm and positive, and so that effect makes sense, too."

Still, said Schwarz, there are caveats. "In some contexts red is a dangerous thing, and in some contexts red is a nice thing," he said. "If you're walking across a frozen river, blue is a dangerous thing."

Indeed, while Elliot praised the Science study, he said, blue's positive emotional associations are considered less consistent than red's negative ones.

It may also make a difference whether the color dominates a person's view, as on a computer screen, or if it is part of what the person sees. Elliot said that in the Science study, it is possible that brightness or intensity of color had an effect, not just whether it was red or blue.

That may explain why results of some studies have been mixed. Some found no effect from color, but used mostly pastels. One found that students taking midterms did better on blue paper than red, but used a depressing blue and an upbeat red.

But in results that appear to align with the Science study's theory that red makes people more cautious and detail-oriented, Elliot found that people shown red on a test cover before an IQ test did worse than those shown green or a neutral color, and also chose easier questions to answer. IQ tests require more problem-solving, similar to the creative questions that Zhu asked.