Highlight invalid fields

[birchamp]

Some of the questions in #377 need to be answered first before moving on this.

Show the user in a performant way that a field is invalid. Perhaps shade the field red or pink.

What kind of invalidation will we look for? Breaks tC - high-priority issues in the validator.
Can this be a component that can work in tCC and gE?
Do we need a collab week?