Indeed, the user does not want to be bombarded with warnings whilst he/she is in the process of creating/updating the entity.
This concept could definitely work, and would be consistent with the existing colour-coding options.
In fact, if formulas were allowed in color coding, then it would become relatively simple to achieve something fairly useful, e.g. highlighting non-compliant entities in table/board/list views etc.
Highlighting specific fields (including when using entity view) would be a bit trickier though.