Apple - How to Invert Color on Mac running Catalina?

I can only use the keyboard shortcut if I go into System Preferences and explicitly unckeck and re-check the box for Invert Colors. Once I am done with my session I enable screen saver by going to a designated not corner. When I come back, the keyboard shortcut only produces the system sound for an alert without inverting the colors. It is again only when I go back into System Preferences and uncheck/re-check Invert Colors will it work again. This is highly annoying and frustrating as I rely on this for various apps that do not have a dark mode in my normal daily workflow.

As discussed in the comment section with @user3439894, we found there're three locations on OS Catalina where you can find the settings regarding to Invert Colors.

1) System Preferences > Accessibility > Display, use the checkbox to manually activate Invert Colors.

2) System Preferences > Keyboard > Shortcuts > Accessibility, use the checkbox to activate shortcut key Ctrl-Opt-Cmd-8 for Invert Colors. Also, do the following in point 3:

3) System Preferences > Accessibility > Shortcut, use the checkbox "Invert Display Color" to use shortcut key Ctrl-Opt-Cmd-8 for Invert Colors.

If you found the checkboxs for shortcut is already checked, but when you press shortcut key and it's not working, try to uncheck and recheck the checkboxs.

I had the same issue. But I found a temporary fix: cmd+alt+F5 to see Accessibility options window, then turn on 'Invert colours'. After that the shortcut will work until next login/screensaver.

I've just reset NVRAM/PRAM and shortcuts seem to work as expected! Finally!