Excel room selection colour coding

Description

Hi All,
I just need a simple excel room availabity auto colour coding. I want to avoid programming and rely soley on Excel colour formatting options possibly with some formulas ( so I can easily replicate this).
I need it where the user selects the rooms from "Select a Room" tab (Columns B, C & D) and any rooms they have selected from the 32 rooms... then the output of the selection in the " Room Availability" tab shows what room has been selected from the available range turns green - thus displaying they are in use.
Any non selected rooms will remain white.
With a count showing in the top left hand corner.
I have an example tab showing how I need it to look.