I’m sorry, I can see now that I did not make that clear. These lines:
“The menu icon color setting works – any changes made there are reflected immediately in the customizer. But changes made to the background color and font color settings have no effect in the customizer or on the page.” was referring to me working in the mobile menu settings in the customizer.
I have been working in the mobile menu settings in the customizer, and only the icon color setting works. The two other settings there – background color and font color – do not work no matter what color I try.