Dorico Pro applies different settings when you export monochrome and color graphics. The most appropriate setting depends on your intended purpose for the graphics.
Most musical scores are monochrome, meaning they use only black ink and are normally printed on white/near-white paper. Some educational books occasionally use colors to highlight particular notations; for example, to identify clefs, or to color notes according to their pitch. If you export graphics files and print them with your own printer, you can leave Color selected in the Destination section.
However, if you export graphics files in PDF format for direct printing on a platesetter or for further production work in a page layout program, select Mono, unless your layout actually contains elements with color or opacity set. If you select Mono, Dorico Pro uses a different color space for the resulting PDF, ensuring that the printed image only uses black ink. If you choose Color, then the black items in your layout are exported as rich black; that is, black produced by combining multiple colored inks. This can cause problems in production when making color separations at the pre-press stage.
Dorico Pro specifies colors using the RGB color model, rather than the CMYK color model that is used by platesetters and other professional printing machines. If you have colored objects in your layouts and your layouts are printed professionally, you must post-process the graphics files that are exported from Dorico Pro in another graphics application to convert the colors from RGB to CMYK.