Hi Miguel - Extended property is fine if there are only 2 colors but If there are 3 or 4 colors then what to do??
You can add extra logic to that if condition but it would be confuse to use and manage.
On your case i would build an action with the function property set to yes so you can call it on the extended property. Something like:
So you would put something like:"background-color = "+GetColorCell(MyParameter)
Let me know if it works.