The Master System already has a green power LED that is not easily changed. It has a green colored window above the LED so putting in a different color LED will only blend with the green window and look wierd.
If you want I can install another LED anywhere and any color you like, or a color changing LED, like this one.
$5 for single color LED.
$7 for color changing LED.
Would like to try to get rid of that green window or maybe just try to illuminate the whole panel kind of like the TG-16 logo light mod.
The Master System already has an a/v out port with composite, RGB, and audio, all you need is the right cord, its the same as the Genesis model 1 a/v cord, find em’ cheap on ebay.
If you prefer the yellow, red, and white RCA jacks I can install them for $25.
S-video is supposed to be almost as easy as composite, if you’re really interested let me know and i’ll try it out.