I am wondering if there is a way to prevent a user from typing in an
Employee's name.

example..

On the left there is a list for Request offs.
On the near right, there is a list of DAY employees with their times.
On the far right, there is also a list, but of NIGHT employees with their
times.

If a user types JEFF in the Request off section, and his name is listed in
the DAY employees section, I want to highlight his name to notify the user
that this Employee has been scheduled when they are not supposed to work.

Is there a way? Also, the list of DAY and NIGHT enployees are used with a
Drop Down menu. Since I know some formulas don't work well when another
formula is used.