ColorBit
ColorBit Select color plane for subsequent drawing short whichPlane ; output plane; (0...31)
ColorBit selects the "color plane" to which Quickdraw should direct subsequent drawing operations. This function is part of the "old model
Quickdraw color support.
whichPlane specifies the plane number. Black-and-white devices have only one
color plane (plane 0). Quickdraw supports drawing to devices that
can interpret up to 32 planes of color information.
Notes: This sets the value of the colrBit field of the current GrafPort structure. It is used for drawing in color while remaining compatible with pre-MacII
Macs. It may also be used in sophisticated applications for creating overlays.