The CGA card used that technique anyway. The IBM CGA card had a 9-pin RGBI digital output and an RCA analog NTSC output. There was a 16 color text mode, rarely used. Color graphics were usually done via the 4 color mode, which chose between four awful pallettes: light and dark variants of white black magenta and cyan, or yellow black red-orange and yellow. So they appeared kinda terrible on an RGBI monitor, but by dithering the colors together and using the analog output, you'd get other colors.