The spinning disk below is a little seizure inducing but a lot of fun because not everyone sees the same color when it spins. Some people see green, others see yellow, a few see red while some see no color at all.
The disk is called Benham's disk. It creates an illusion of color when black and white patterns rapidly change (even when there are no colors at all in the image). We're imagining color where there's no color to see.
The phenomenon is not entirely understood. One possible reason people see colors may be that the color receptors in the human eye respond at different rates to red, green, and blue. More specifically, the latencies of the center and the surrounding mechanisms differ for the different types of color-specific ganglion cells.
I got yellow and a little bit of brown.