Attract color shifter; the color registers are EOR'd with locations 78 and 79 at the stage two VBLANK (see locations 18-20;$12-$14). When set to zero and location 78 equals 246, color luminance is reduced 50%. COLRSH contains the current value of location 19, therefore is given a new color value every 4.27 seconds.

See also:

ATRACT, DRKMSK