I'm just an amateur. I recently found how to change the default colors in a notebook using "Edit style sheet" in "Format." I am currently using my own color set to "Appearance" in "Preferences" along with a custom style sheet and code
SetOptions(EvaluationNotebook(), Background -> Black);
(Side note, I deliberately avoid the "ReverseColor" ability because it doesn't give me very fine control over my colors).
By doing something in the line of …
a="String length:"; Print(a,"= ",StringLength(a));
How do I get the default printed text / result to be a color that is not black?
Can I do the above and also change the default background for a notebook using only the style sheet and the appearance settings?