If you are using your Hacktintosh to just check email once in a while, this post is not further importance to you. However, if the computer is used for any sort of visual work, such as processing of video or still photography, artwork or design, you may want to consider calibrating you screen.
Of course there is the relatively pricy option of screen calibrators which you connect via USB and all the magic happens.
As to Apple's OS-X, there is a calibration mode provided for free, which uses even more precious sensors, namely your very own eyes.
For using this tool, you want to open the "Displays" option in "System Preferences". Go to the "Color"-tab. Now you want to click on "Calibrate...", which will open another window. Be sure to check the "Expert mode" box! As of now, lean back (as the instructions will tell you) and follow the instructions!
My experience told me to do this exercise a couple of times in order to get the hang of the tool and a precise calibration. Mind you, you are using parts of your very own body to calibrate an electronic device. Using your senses always involves learning.