CreateEvent - color field

Right now, the form submit a hardcoded 'Colors.RED' as the event's color. There's a colorpicker element which we could use, but I think it should be discussed whether we want the users to have that much freedom in choosing an event's color.
If we remain on the original enum approach, we need to validate the users' input on the frontend.

Start by locating the CreateEvent form and the code that currently submits Colors.RED. Review how the colorpicker is wired, then clarify whether users may choose arbitrary colors or only enum values. Done means the chosen policy is implemented and frontend input validation is covered.

Written by the indexing model from the issue text.