I don't see any color at all...

I don't see any color at all ... do you?  This optical illusion is called Benham's Disk (after the discoverer, an English toymaker).  Most people see some pale colors when the focus on different parts of the disk – but the perceived color varies from person to person.  Some people (including me) see no colors at all.  Nobody seems to understand where the colors come from (as the disk is just black and white), why different people see different colors, and especially why some people see no colors at all...