The macro is a change event macro, meaning that it runs when a change occurs in a cell on the worksheet it is attached to.
Nothing will ever happen if it is in a Module.
Select the worksheet containing the 270 values.
Right-click on the name tab at the bottom and select 'View code'
In the Visual basic window that opens make sure that the window is empty - delete any code present.
Then copy the whole of the code I submitted, from Option Explicit to End Sub (inclusive) and paste it into the Visual Basic window.
Use Alt+f11 to go back to the main Excel window.
Click on any empty cell in the worksheet and enter something and click enter. The 270 cells should change color.
If nothing happens, it is possible that Events are disabled.
In The Visual Basic window, from the Menu bar, select 'View' and 'Immediate Window'. In the Immediate window that opens, scroll down to the bottom of the list and enter:
Application.EnableEvents = True and click Enter, and test again.
If it still does nothing, add a Break Point to the code (at the For Each rngCell ... line) and see if it stops at that point.