Calibration Tool for your monitor on Linux

Nice Python tool to calibrate your monitor: Gammapage


http://www.pcbypaul.com/software/GAMMApage.html

You also can use xgamma for doing this at startup:
Go to System. Preferences, Sessions.
Choose Add
name: xgamma;
command:

xgamma -gamma 0.86

This is of course a choice you have made earlier for example with the tool Gammapage.
Now every time on startup your gamma will be reset by xgamma.