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I'm using Ubuntu 11.10 and my monitor had a problem where Green is the bright colour, there's no way to change it in the monitor settings, so when I was using WinXP (I'm new in here) I changed the green to lower using Video Driver settings, in here (ubuntu) I don't know exactly how I would change the green colour to low, so my "black" would be seem has a real black, no green. Thanks for reading. Sorry for bad English.

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You might be able to adjust it with the xgamma tool (in particular the -ggamma option). I'm not sure how well this would help with the green brightness for black pixels though. –  James Henstridge Apr 9 '12 at 5:16
@JamesHenstridge, works fine, thanks. But you commented in here, so how may I give you the best answer? –  PedroGabriel Apr 10 '12 at 21:34
Glad it helped. I've added an answer based on the suggestion, along with some tips to apply the setting each time you log in and how to handle multiple monitors. –  James Henstridge Apr 11 '12 at 6:30
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You can adjust the individual colour gamma correction settings of your screen using the xgamma tool. Running it with no arguments will print the current settings:

$ xgamma
-> Red  1.000, Green  1.000, Blue  1.000

You can adjust the green gamma value with a command like:

$ xgamma -ggamma 0.75

If you are using a multi-monitor set up and want to adjust the gamma of individual outputs, you can do so with the xrandr tool instead:

$ xrandr --output $OUTPUT --gamma $RED:$GREEN:$BLUE

In this command, $OUTPUT is one of the outputs listed when you run xrandr with no arguments. Note also that xrandr treats the gamma mapping as going in the reverse direction, so you will need to provide the inverse of the values you'd provide to xgamma (e.g. passing 2.0 to xgamma is equivalent to passing 0.5 to xrandr).

Both of these options will not survive an X server restart, so once you've got some values you're happy with consider putting them in a shell script (perhaps in ~/bin), and then adding that script as a startup application.

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I have a toshiba satellite l675d laptop. here is what worked for me.... from terminal, "xgamma -rgamma 1.05 -ggamma 1.10 -bgamma 0.70" great, now have a nice grey.

but how to save this so it executes on startup?

I have tried the unity startup app. I can enter the the script, save, etc. After startup, in terminal, I can see the new settings as above. BUT the monitor is NOT adjusted - it has the regular default colours. I can adjust only after manually entering the command in terminal after startup.

Can anyone help please?

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