Professional 4-color printing is done with MCYB (magenta, cyan, yellow, black), while color television (or computer screens) is usually done with RGB (red, green, blue). I'm not sure precisely how to translate RGB to MCYB, but I think an approximate color mix is: Official Color Description RGB Mix Name Magenta Hot Violet Red+Blue, No Green ?? Cyan Aqua Green+Blue, No Red ?? Yellow Yellow Red+Green, No Blue ?? (Kate says Magenta is a kind of cool red, or better, azelia fucia.) If you specifically want to print a 24 bit color image on a monochrome printer, one of the postscript utility files says that the color information is converted to grayscale intensity values using the CIE formula: intensity = .299 red + .587 green + .114 blue