Changing cell content based on it's inclusion on a list

So i'm very green with Excel and can't find the right way to ask this to get an answer on Google...

I have a selection of cells 200 x 200 to represent the pixels on an LED wall module.

I would like to create a simple visual reference for faulty pixels.

To that end when a pixel is working (default) then the cell will contain a '.' and be green.

To change from that I would like to be able to put a cell reference into one of 7 lists - No red, No blue, No green, Red only, Blue only, Green only or Dead.

The relevant cells will then change to a specified content - an "X" - with the colour of the cell changing to one relevant to the list (e.g. no red turns yellow, or red only turns red).

I can't work out how to reference the cell addresses in the lists to influence their content.

Working on Excel for Mac Version 16.108