When I was in grad school we always added tetrazolium tetrachloride to our minimal plates because it makes the colonies red and easy to see. I couldn't find any instructions for using it in minimal plates but I found old (Lederberg-old) instructions for using it in nutrient agar, so I used that concentration.
Now I just need to wait for the colonies to grow. That will be slow because they're on minimal agar, so they probably won't be countable until tomorrow. I can spend the intervening time helping grade my last exam question and entering the numbers into my spreadsheet, and then doing the Excel-wrangling to get the final grades for my ~400 freshman biology students.