IIRC, it shifts them half a pixel, regardless of whether it's color or monochrome, and that's why it affects the palette. In color mode, the on/off pixels form

IIRC, it shifts them half a pixel, regardless of whether it's color or monochrome, and that's why it affects the palette. In color mode, the on/off pixels form a psuedo-sine wave, and the phase of this wave determines the color: if it's on even pixels you get green, if it's on odd you get purple, if it's on even-and-a-half you get orange, and if it's on odd-and-a-half you get blue (give or take which alignments are even/odd and half/whole, since I can't remember, but that's the basic idea).