Color management is inherently different on Mac and PC. It is also different if you want to correct for web or for printing on an Epson printer for example, or at a print plant in CMYK. On the two machines: you MUST calibrate the monitor, using ColorSync on Mac and Adobe Gamma on PC. Set the temp color of the monitor to 6500K. It's the same as the sun, so when you'll modify photos on the screen, you'll be with a correct setting. On the PC: for web, the color space is, now, sRGB in 24 Bit systems, and the 216 Web Colors in 8 Bit systems. On the macintosh: the same apply. Of course, if the monitor of, say, somebody browsing the web is not calibrated, the colors will be bad and you can't do anything to that. In printing on a Epson or similar printer, you must understand that the printer is RGB, as the screen. You must chose the correct settings corresponding to the paper you use and then the driver will do the correct CMYK (or else) separation to send to the printer. But you must keep in mind that the Epson system is RGB. If you'll print at a print plant, first call them and ask for details about CMYK separation. They will flash your files and know these settings. You'll then set them in Photoshop preferences. Feel free to email me.