When troubleshooting a misbehaving application one thing I learned early on was to go to the user’s home folder, and find the application’s preferences file (.plist) in the Library/Preferences folder, and drag the file to the desktop (bin it later). This often has a miraculous effect after restarting the application.

Other corruptible files are in the Application Support folder in the user’s Library folder, and the one that solved a problem today: removing the relevant cache file in Caches, again in the user’s
Library folder.

That one got InDesign working properly again when the color picker became stuck on pantone only. I had begun to wonder what to do, but was reassured when I logged in as Guest, started InDesign, and all was well. That proved that the problem was with the user’s settings and not the application proper.