Specific Changes to Comobox Selection?

I have created a combobox in Excel and in need of changing a specific selection to have a back fill of yellow.

For example: my combobox has a list of PTO, OT1, OT2, PHOL, RED
I need to figure out how to have a backfill of yellow when OT1 or OT2 is selected?

Im not sure if this is even possible, I am a little rusty at Excel so any help or insight is much appreciated.


Is the combobox placed on a

Is the combobox placed on a userform or is the combobox placed on a worksheet?
And what need to be backfilled? The combobox or a cell on a worksheet?