
These impossible colours exploit the (amazing) neural processing that happens within the retina. There's a kind of antagonism between colours that means you never see a reddy green for example, because a red response antagonises green. But by stabilising different images on each eye you can (in a sense) circumvent it. So much incredible processing of our cone responses happens after the signals have only travelled through a layer of three neurons within our eye, before the signal even enters the optic nerve.
Magenta is fascinating too - in that it doesn't correspond to any wavelength (isn't in the rainbow), but rather occurs because of another artefact of our retinal processing. Also, magenta cocks. Naturally.
( , Thu 18 Sep 2014, 1:15, Reply)

Sorry, I went off on one a bit there. Here is a good video about magenta:
youtu.be/iPPYGJjKVco
( , Thu 18 Sep 2014, 11:36, Reply)