Improve NTSC artifact colors

[craigthomas]

The emulator currently takes a fat pixel approach to emulating artifact colors. It performs a very rough approximation of whether to draw a red or blue pixel depending on the alternating patterns of black or white. While this does the job of incorporating colors into the display for artifact color modes, it appears blurry (the transition between colors in a true NTSC display would be more gradual with better gradation between pixels). The purpose of this enhancement is to generate a better drawing method that takes into account how NTSC artifacting works.