Examination of the receptive field structure of the retina suggested looking at small graphic figures of special forms. The luminance distribution called the "Mexican hat function" was approximated by a black dot with a small white dot at its center, called a "tip," and the inverse function was approximated by a white dot with a small black dot at its center, called a "pit. " Such figures were given the generic name "tippit. " On a dark-blue ground, tips looked yellow, and on a bright-yellow ground, pits looked blue. Similarly, a black line with a white center, on a blue ground, and a white line with a black center, on a yellow ground, elicited these effects. On yellow and blue grounds, simple, small colored dots looked more like the color of the ground than when seen as large spots on a neutral gray ground, an effect here called "microspreading. " This effect may be attributable to scattering and blurring, but these processes do not account for the tippit effects. The visual system exaggerates contrast between a large spot and ground, and diminishes contrast between a small dot and ground, but exhibits neither effect on a figure of some intermediate size. Chromatic pit lines exhibit effects obeying laws of additive mixture. It appears that perceptions of these effects are normally repressed. No causal link was sought or established between receptive field theory and the observed effects. (C) 2003 Wiley Periodicals, Inc.