[albert_e]

The illusion was very strong on my mobile screen and non-existent on my desktop screen. The screen calibration was different in the latter I believe so the pigeons were appearing as a slightly different colored grey blocks visually distinct from the vertical bars.

[jrumbut]

Funny, I still get the illusion after turning the pigeons every color from dark grey to bright yellow.

Brighter colors make it a bit less strong but still very much there.

[Enginerrrd]

On my laptop, I am only able to see the illusion if I looked at the striped background and blur my vision a little. Then it is quite impressive and strong. Otherwise, it always appears perfectly smooth for all colors.

[daveslash]

I get the illusion for yellow, but not for bright red or blue. That's interesting....