Comment 5 for bug 1507674

I thought about warning in non-obstructing way. Something like these:
https://m2.behance.net/rendition/pm/20560631/disp/efc6e2963310777d0365d06689f2619b.png
Maybe it should appear for single objects only, not for groups, assuming that if user changes color for group, he knows what he's doing.