For colorcop I have to activate the filter JqueryUI in WB 2.11 at Output Filter Frontend. This filter was not present at WB 2.10
If I add an extra image after activating JqueryUI in the relevant page, then colorcop will no longer work.
To add an additional image, first disable JqueryUI and re-enable JqueryUI after adding the image.
In this way, colorcop works fine with me.