A monitor's gamma correction

user@host:~$ xgamma
-> Red  1.000, Green  1.000, Blue  1.000
user@host:~$ xgamma --help
usage:  xgamma [-options]

where the available options are:
    -display host:dpy       or -d
    -quiet                  or -q
    -screen                 or -s
    -gamma f.f              Gamma Value
    -rgamma f.f             Red Gamma Value
    -ggamma f.f             Green Gamma Value
    -bgamma f.f             Blue Gamma Value

If no gamma is specified, returns the current setting
user@host:~$ xgamma -gamma 0.6
-> Red  1.000, Green  1.000, Blue  1.000
<- Red  0.600, Green  0.600, Blue  0.600