Now that we know how the graphics worked on the Nintendo Entertainment System and Commodore 64, The iBookGuy wants to tell us all about how theApple II and Atari 2600 got their groove on. In the he says that the Apple II actually used two different techniques for producing visuals depending on whether you had a monochrome or color monitor unit. And the reason white text on a black background appears almost rainbow-like in nature on color machines has to do with pixel placement. For example, blue and green being next to each other on screen requires perfect alignment lest you want white mages to have spots of the former bleeding into them.

http://www.engadget.com/2015/08/31/a...ics-explainer/