In the research described in this article we have tested the idea that the recovery of depth and orientation of twodimensional patterns is aided by constraints in the physical world. We presented a variant on a bistable Necker cube. the surfaces of the cube were constructed from transparent planes. We examined which color compositions lead to the highest number of correct identifications of orientation. the results can be explained on the assumption that people use constraints present in additive color mixture. When this type of mixture is used, it leads to significantly better responses. the luminance of the mixed color is the largest contributor.