Hi matfer. This is part of the notes for “New: Physically Based Default Post-Processing Settings”. For now you should be able to restore the original look by following:
You can switch the tonemapper back by adding r.TonemapperFilm=0 to the SystemSettings section of your project’s DefaultEngine.ini.
We hope to provide more detailed information about this change in an upcoming learning resource.
EDIT: I didn’t refresh the page and kgamble beat me to it.