The aim of this study was to explore how the ratio of size and the background color of foveal and peripheral windows affect ed the work efficiency at the foveal window. On the basis of the results, an attempt was made to clarify the cognitive layout of multiple windows that makes the visual interference minimum. It was clarified that the area ratio of the peripheral window to the foveal window was one of the determinant factor that affected the visual interference. Moreover, it was found that the visual interference occurred not during the perceptual process, but during the cognitive process. It was also indicated that the background color on the peripheral window did not affect the visual interference. The background color on the foveal window seems to affect the counting accuracy on the foveal window according to the attractiveness of colors. Some implications for designing multi-window systems were given.