Select the field in layout mode that is to change (A), base the Formula on the other field (B). Select the color of the background.
You will see a "badge" on the field (A) showing it has been conditionally set. Yes, you can add more than one condition.
See this thread for a sample database file when I created a conditional on a text object based on a field:
the principle is the same using two fields.
Thanks Beverly, works fine!