The color of the overlay probably changed because you pressed Shift+O, which will cycle through the colors available - I doubt that this is related to the problem.
Another thing to try is resetting the preferences.
Press Ctrl + Shift (Option + Shift on a Mac) immediately after clicking the shortcut to launch Lightroom.
A dialog will appear asking if you want to delete the preferences. Click Yes.
This procedure can be a little tricky, so if you don't get the dialog, delete the preferences file manually (with Lightroom closed).
Here's instructions on where to find the file: Preference file and other file locations | Lightroom Classic CC and Lightroom 6
Note that if you have a Mac, a computer restart after deleting the preferences is required.