Motorola 6847

The MC6847 is a video display generator (VDG) first introduced by Motorola and used in the TRS-80 Color Computer, Dragon 32/64, Laser 200, TRS-80 MC-10, NEC PC-6000 series, Acorn Atom, and the APF Imagination Machine, among others. It is a relatively simple display generator compared to other display chips of the time. It is capable of displaying text and graphics contained within a roughly square display matrix 256 pixels wide by 192 lines high. 
It is capable of displaying nine colors: black, green, yellow, blue, red, buff (almost-but-not-quite white), cyan, magenta, and orange. According to the MC6847 datasheet, the colors are formed by the combination of three signals: Y (6 possible levels), phiA (3 possible levels) and phiB (3 possible levels), based on the Y'UV colorspace.
The low display resolution is a necessity of using television sets as display monitors. Making the display wider risked cutting off characters due to overscan. Compressing more dots into the display window would easily exceed the resolution of the television and be useless.
Y'UV levels.
According to the MC6847 datasheet, colors are formed by the combination of three signals: Y, phiA and phiB, according to the Y'UV colorspace.
Y may assume one of these voltages: "Black" = 0.72V; "White Low" = 0.65V; "White Medium" = 0.54V; "White High" = 0.42V. 
phiA and phiB may be: "Output Low" = 1.0V; "R" = 1.5V; "Input High" = 2.0V.
Hardware Color palette.
Colors generated by the hardware, adjusted for maximum brightness.