The color facilities are available only under X-Window systems. Moreover, not all X-Window like devices recognized by GREG effectively use the color for bitmaps. Only the DEVICE IMAGE does. This restriction exists because the color map allocate by GREG is a private color map. As a consequence, no more than a single GREG with DEVICE IMAGE can operate at any one time on an X-Window terminal. The pencil colors (pencils from 8 to 23) can always be edited. The number of bitmap colors is usually 128, but can be less if many color applications already use most of the available colors of the X-Window terminal.
For hardcopies, color is supported only the PostScript format. Two options exists for the type of PostSsript created: GREY or COLOR. The GREY version, used by HARDCOPY /DEVICE PS GREY, has a fixed transfer function of greyscales. The transfer function is non-linear, and reasonably suited for most astronomical images. The LUT command has absolutely no influence on this type of HARDCOPY. The COLOR version, used by HARDCOPY /DEVICE PS COLOR, uses the current LUT to produce the PostScript output. On Greyscale printers, the colors are converted to grey intensities using standard formulas (what you would see by replacing a color display by a monochrome one). Colors are used on color printers.