On most occasions you'll want the colors in your document to be separated as process colors-combinations of cyan, magenta, yellow and black which together result in the range of colors in an image. But some colors are difficult to achieve using process color combinations: it may be easier to have the exact color of ink mixed especially and printed as a spot color. Spot color is also often used with fine lines and small text, which can 'break up' if printed with process colors.
Each spot color requires its own separation plate. RSG lets you change any specified color (except individual colors in a picture block) to print as a spot color.

You can also print any picture in a picture block in a specific color, spot or process, by assigning it to that color separation plate. The picture will then print as shades of the chosen color.
And if an EPSF image file in a picture block includes spot or process color information, RSG can use that information in making the separations. This lets you combine both spot and process color separation within the same image.