Is it possible to change the color model of an entire QGIS project from RGB to CYMK? I know that it's possible to change the color models of individual symbols/features (through the style manager), but I can't seem to find an option for the whole project. While my workflow usually sees me polishing my maps in Inkscape/Illustrator (where it's easy to switch between RGB/CMYK), it would be nice to have the option in QGIS as well.
CMYK color space is not currently supported for any export file types.
When defining individual symbols/features using CMYK, the color values are always (from what I know of the code base) stored as RGB components, pulled from the QColor returned from the color picker. The fact that you can choose to define those colors using CMYK is an isolated function of your OS's native color picker, which is used for all color picking, and not indicative of support for that color space in QGIS.
This is not to say that CMYK outputs can not be supported. You might consider adding a feature request to the tracker.