Background Color Keyword
Switch and parameter that specifies the background fill (erase) color, default is white (255255255). N1 is a kilo color spec
when only one number is present otherwise all three numbers must be present and
they are an RGB triplet where each gun has legal values from 0 through 255 (ie
N1 is the red gun value,
N2 is green and
N3 is blue). Similar to the <WritingColor> switch, when used as a parameter it sets the default background fill color for all frames, when used in a frame it sets the background color for just that frame.