We sometimes can recognize the color which should not be expressed by the ink set of only two colors. Remarkable example is seen in prints made with ink set of cyan (C) and magenta (M); they look like rather regular full-color prints and missing yellow (Y) color is often recognized in the prints. We have reconfirmed quantitatively that humans can perceive "impossible" colors in prints that were created with just two colors: most subjects perceived "yellow" in those prints. We suppose that our natural color constancy works when we recognize two-tone color prints. We attempted to explain the reason by considering the von Kreis model, which describes the chromatic adaptation to changes of lighting conditions. Using the von Kreis model for C+M-prints showed good estimation of the original color of the reference C+M+Y-print. We have confirmed that this effect is likely to be due to a compensation mechanism that is similar to the one that allows color recognition under a colored light. We conclude from this result that C+M-prints tend to look like full color prints because we can easily compensate for the missing color in C+M-prints by only using the linear gain-control mechanism at our natural vision system.