It's like using the colour attribute specification (as on [[ZX Spectrum]]) but with horizontal limitations.
Basically a an "upgraded" '''CGA ''' standard PC video display.
Pictures and graphical materials have to make good use of [[Dithering|dithering]] in order to get a realistic look, yet the square pixels allow smooth dithering, and the absence of colour attribute system permit really interesting stuff compared to the humble speccy.