8-bit color is for the total indexed color spectrum per pixel for a video card. Since we are talking about screens, 6 bit is per channel, 6 bits for red, 6 for green, and 6 for blue.
In 8-bit indexed color, the color palate for video cards may be changed to a different set of colors depending on the application. The screen can obviously display many more than 256 colors, but the video card would limit it to 256 at a time.
Ahh, I thought they meant six bits per pixel, not per color plane. Makes sense. THanks to you and the others who answered me.