Something Profound Going On?

An exercise in third eye vision

I visited the Synergetics site today, and happened across a page of stereo viewing techniques. http://www.wolfe.net/~setebos/springspace.html Seems by crossing one's eyes the right amount, a pair of identical pictures will merge into third three dimensional view. So I thought I would try it with our gestalt figure, the (s) Icon. . Cool. it works.

But even more interesting,
I was fooling with the colors, and tried a blue and a yellow, thinking I would get green. BUT I can't see the yellow? The blue wants to dominate! If I force myself to see yellow, I can only for a split second, then it paints itself blue again. Why? Is perception colored?