Somewhere between versions 42 and 46 of gnote, the background color for text highlighting changed from yellow to blue. It’s impossible for me to use that way, so here’s how you can change it back to the way it was, with a yellow background and black text:
You’ll need to edit two gsettings. I found the easiest way to do this is with the dconf editor (from the dconf package in Debian). In it drill down to: org / gnome / gnote then edit org.gnome.gnote highlight-background-color ‘#FBFF00’ for yellow, and org.gnome.gnote highlight-foreground-color ‘#000000’ for black.
Love gnote!