When CMYK is an option in your GIS, you may want to use it if you are con‑
cerned about matching the look of the color on the screen with the color on a printer.
However, you have to be cognizant of how your GIS exports color. Just because you
defined a color in CMYK does not necessarily mean it will be exported in CMYK.
In fact, some software will convert your color definitions to RGB when you export.
This is mainly a concern only for those people who are sending their file off for
offset (commercial) printing. If your software exports in RGB, a way around it is
to export to graphics software like Adobe Illustrator or Adobe Acrobat, change any
colors that changed, and then export to a printing file format from there, specifying
CMYK mode. Another option is to print out a conversion sheet that shows what a
color looks like on‑screen with what it will look like on a printout.