invert colors on X (or xfce4)
You need the xcalib package:
xcalib -i -a
If you are like me and you have tried xcalib but you have encountered an error like this on debian:
xcalib: unsupported ramp size
Then you could use an alternative like: xrandr-invert-colors.
First clone the repository
git clone "https://github.com/zoltanp/xrandr-invert-colors.git"
After that you can install the build-essential package and you can compile the code with that commands:
sudo make deps-apt
make
sudo make install
After that inverting colors on the screen is simple as:
xrandr-invert-colors