How to remove material theme (or reset to defaults) from IntelliJ / PyCharm?

you can go to the Preferences->Plugins on the search bar, type Material UI then press on the Uninstall button .

You should:

1. Go to Settings->Plugins and remove Material UI plugin
2. Switch to Default theme in Settings->Editor->Color Scheme

If it does not help (it happened to me) and you still have some colors/fonts from removed Material UI - looks like Material UI theme override some default colors. You should then close Intellij, go to Intellij config folder (on Windows it is C:/Users/<your username>/.IntellijIdeaXXXX.X/config) and remove this config folder and restart Intellij. It should show you a dialog window to import settings from previous version or use defaults (like when you install Intellij and make the first start). After that everything will be switched to default colors/fonts.

From the material-theme-jetbrains repo:

File Colors stuck after uninstallation The File Status Colors feature is also a feature that sticks outside of the realm of the plugin as it modifies the IDE itself. Therefore when uninstalling/disabling the plugin the colors will stuck.

If you want to reset to the default colors, open the Settings at Version Control -> File Status Colors in 2017.3+. In previous versions, you will need to go to the config directory and delete the _@user_Darcula.icls color scheme manually.