How to highlight a wrong value based on two text cell. workplanner

Hello,

 

I want to upgrade/modify this sheet so that I can use this, related to my job. But I have an issue which I can't find out.

 

I want to highlight a cell which is depending on two other cells.

Within my attached sheet I want to highlight a cell when I choose by accident a colleague who is sick or on leave.

 

So a little bit more explanation

 

When as an example Sien is sick. And I will create the workschedule for the early shift at row b-cel. I want to highlight my mistake. Or I want to have Sien removed from the dropdown menu.

 

Maybe I should create a calendar to automatic fill out the available, leave, sick field at the personal part. But i have no idea how to do this.

 

A person can't work on two locations so when I choose two times the same person it will be highlighted. that's working.

 

please help me to get this done, all other suggestions are welcome as well.

 

THANKS IN ADVANCE!!!