This experiment ilustartes how color can impact our spatial perception. Regulating the middle slider, located on the bottom, can change the perceived "transparency" and relative "position" of the two rectangles. Also you can change the colors of these recatangels by adjusting the side slider. 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 look of "opacity" and "occlusion." In addition there are four preset color groups located on the top.