Use xbacklight to change brightness, and xgamma to change color. For instance, if you wanted a more "cool night" glow, you might run this:

xbacklight -set 60 ; xgamma -ggamma 0.8 -rgamma 0.8 &> /dev/null

And then for daylight, you might run this:

xbacklight -set 100 ; xgamma -gamma 1.0 &> /dev/null

i don't know what it really does, but if it's just dimming the screen at certain times, call xbacklight from cron.