Color stimuli (IMAGE) NIH/National Eye Institute Caption Colored stimuli in yellow (top) and blue (bottom). Light luminance level versions are on the left; dark versions on the right. Volunteers used a variety of names for the upper stimuli, such as "yellow" for the left and "brown" for the right, but consistently used "blue" for both the lower stimuli. Credit Bevil Conway, Ph.D., National Eye Institute Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.