Show term color inputs immediately for taxonomy terms

Problem/Motivation

The ability to assign colors based on taxonomy term was added in ✨ Ability to choose event color according to taxonomy Active . The compomise made in that issue, however, was that after choose a vocabulary, the site builder sees a message advising them to save and reopen the settings to see the choices.

In earlier commits the input did show immediately, but weren't saved. This would seem to because of security features in Form API, which prevent any values being saved that weren't part of the form structure when created.

Proposed resolution

Devise a way to show the inputs immediately, and have their values saved. This may require some R&D.