Oh wow, thanks for this one. Immediately noticed a reduction in eyestrain. If you're found the GUI buggy (as I did), try the command line interface (xflux). The CLI app works fine for me.
Has helped fix me off of getting off the computer at night with the color/gamma changes.
Unfortunately I couldn't get it to work* on my Ubuntu box and found another app, Redshift, that seems to jive better with Linux: http://jonls.dk/redshift/
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* Ran without errors, but didn't tint my screen. I chalked it up to oddities of video card drivers on Linux.