
Ronald M. answered 12/08/20
Experienced Illustrator User
The best way to add a "colored background" in Illustrator is to create a colored rectangle that goveers the entire artboard. There's really nothing in the preferences to set a colored background.
I usually cover the entire artboard (including the bleed area with a colored shape) and lock that layer. That's what I normally do for t-shirt mockups and logo presentations.