Comment # 1 on bug 955069 from Wolfgang Bauer

(In reply to Stanley Miller from comment #0)
> When trying to set the gamma video settings in the desktop settings program
> I get a message that xf86gammacfg could not be loaded. 
> 
> It isn't on my system (fresh install of leap 42.1) and it isn't listed as
> included in kgamma5 but is in the file list in the old kgamma program.

xf86gammacfg has been removed upstream when kgamma was ported to KF5.
It didn't really work since years anyway, as it requires an existing xorg.conf
which normally is not there nowadays.

But, xf86gammacfg is only needed if you want to save the settings systemwide.
Just deactivate that checkbox (it has not been removed for some reason) and you
should not get an error.
And the settings should be applied when the user logs in.

Anyway, this is an upstream issue.
Feel free to report it at http://bugs.kde.org/.