The function to change the font color appears to have been disabled. Neither right-click-character nor menu-format-character are able to get the color of the character to change! Yes, I highlighted the characters, just like bazillions of times in the past.
Hi, Hmmm.. maybe try a fresh user profile? No idea. It just works here. Maybe a special document?? Then our community-support gives abundant help probably. Sorry - Cor
It could be accessibility thing. Check under Tools->Options...->LibreOffice->Accessibility, that "Use automatic font color for screen display" is not checked. If it's checked, uncheck it and restart the app.