[zootboy]

I wasn't too impressed with this one, either. In my mind, this illusion is much more straightforward demo of a similar effect (color perception being relative to surrounding colors):

https://www.illusionsindex.org/ir/checkershadow

[delarge]

The shoe example seems closer to a weaker version of this effect: https://www.illusionsindex.org/i/grey-strawberries

[jaclaz]

Yep, and it works for grey scale too.

This is the one I find the simplest:

http://3.bp.blogspot.com/-FLbAdn2URJs/Toim-B864TI/AAAAAAAAOc...

And a video of a similar effect:

https://www.youtube.com/watch?v=z9Sen1HTu5o

[notfed]

Yeah, this one is a true illusion: they're actually the same color, unlike the shoe example.