Conditional Formatting formula to highlight a column if multiple criteria are not met.

Hi,

I'm working on a work schedule spreadsheet for my place of employment. We have 4 people working each day on 2 shifts. (2 people on shift 1 and 2 people on shift 2). I am trying to figure out a formula to highlight (conditional format) the column for a given day if the scheldule is not correct. I kinda figured it out using the following formula =SUM(COUNTIFS(B3:B16,{"1","2"})). This does work if there is too many or not enough people working. But it dosesn't if there are 3 people put on shift 1 and one person put on shift 2. I provided a screenshot of what I'm trying to do, so hopefully, it shows up. Basically, I need a formula so that if cells B3:B15 don't have 2 cells that contain just the number "1" and 2 other cells that contain just the number "2" format it red. I've been working trying to figure this out for a while so any help anyone can offer would be greatly appreciated.

Thanks and have a great day!

FDibbins, thank you so much! This formula works perfectly and was exactly what I was looking to do. I'm not that good with formulas, but now I see the correct formula it makes sense. Your assisstance is greatly appreciated!