This program demonstrates how color can influence our spatial perception. Adjusting the "middle color" slider can change the perceived "transparency" and relative "position" of the two rectangles. For example, if the left and middle hues are identical, the left rectangle will appear both "opaque" and "in front of" the right rectangle. Subtle changes in the middle color can dramatically change the appearance of "opacity" and "occlusion." The blue presets demonstrate how a small color change can make one rectangle appear to come "out in front" of the other.