Wow! After you said that, was your next thought How? If so..read on.

Pink , or officially, magenta, is not a “real color”..there is no wavelength in the electromagnetic spectrum assigned to it. We see it because our brain interprets more than one input, in this case red and violet at once, as a new color pink (green and red seen together gives yellow). So, why the green afterimage ? Turns out that green is the perfect complementary color to pink (you may have thought red). Check this link for the explanation:

http://www.null-hypothesis.co.uk/science/strange-but-true/colour_spectrum_magenta_complimentary_bizarre

Originally shared by John Baez

Stare at the + sign. Don’t let your eyes move off that + sign, no matter what you see! If your eyes move, go back to looking at the + sign.

I seem to have lost track of who on Google+ first pointed this out. Sorry, but thanks!