In (computer) graphics, the alpha value of a given pixel governs how transparent it is and the gamma value of the monitor governs how bright it is. I presume beta is assigned to something (value or hue, perhaps?) and maybe epsilon and beyond are as well. Are they?
Nope.
How… existentialist. 
Why was beta skipped? Bad memories of the video wars?
Gamma came from physics and other scientificey origins. Alpha was a graphics geek hack.