Optical illusion...

[begin_within]

Look at the image below three different ways:

If your eyes follow the movement of the rotating pink dot, the dots will remain only one color, pink.

However if you stare at the black "+" in the center, the moving dot turns to green.

Now, concentrate on the black "+" in the center of the picture. *After a short period, all the pink dots will slowly disappear, and you will only see only a single green dot rotating.

There really is no green dot , and the pink ones really don't fade to gray. This should be proof enough, we don't always see what we think we see.

[ghostsofgiants]

1. Neat.

[marzipanni]

2. That's weird

I saw the green dot going around, but then went cross-eyed (?) and saw two "+"s in overlapping circles of pink dots.
Looking at it with one eye, the effect you described worked, looking at it with either eye, or both.