Working with indexed color channels
By default, when you print color separations from QuarkXPress using PSD Import, the colors in indexed color images separate to CMYK. You can override this by creating a spot color or multi-ink color (Edit > Colors) and assigning that color to the selected indexed colors in the image. PSD Import also allows you to create spot colors from colors in the indexed color image. Indexed colors that you do not modify will still separate to CMYK.
Parent topic: Working with PSD channels