I am using 2 screens, and wish to invert the colors on both of them without using compiz (I'm using gnome shell).

I can use xcalib -invert -alter as suggested in this question, but it only inverts one of the screens. Is there a way to specify both of them, or even which of them, using xcalib? Is there another way?

With xcalib, you can specify which screen to alter with the -d (-display) or -s (-screen) options, but alas, X seems to be aware of just one screen: when I use the w command I only see one (the usual ":0")

ps: this question was originally posted by k0pernikus as a comment here.