The main link goes to https://www.dropbox.com/sh/oi9wdd0uc5uc ... 0tma?dl=0. , which offers a bunch of images and brief explanations to go with them.
Various documentation says
Here is one illusion that I found very impressive:David Novick, @NovickProf
Department of Engineering Education and Leadership
The University of Texas at El Paso
http://engineering.utep.edu/novick/
http://www.engineering.utep.edu/novick/colors/
This one is titled "Large spheres blue-green", and that is exactly what I see: one blue sphere and one green sphere, overlaid by a bunch of colored dots.
But the bodies of the spheres are in fact exactly the same colors, as I confirmed by loading the image into Photoshop, magic-wand selecting the yellow and purple background colors, and converting those pixels to a uniform gray.
For me the illusion is totally compelling. I simply cannot see the two spheres as being the same color, no matter how hard I try to focus attention on the spheres and not the colored dots.
--Rik