Implementing RAG on Excel based on dates passed

Hi, 

Im struggling to implement a red, amber, green system on Excel on a project for work (I have very limited Excel knowledge). 

The system relates to how long patients have been admitted to our service. If they been there 1-2 days = Green, 3-4 = Yellow and 5+=Red. 

The two columns I'm comparing Are "Arrival Date (C2:C8)" and "Anticipated Exit Date(D2:D8)" but am struggling to have the anticipated exit column display the relevant colours. 

Here's a screenshot of what the table looks like when filled out manually:

Any help on how I might get the final column to assign a colour automatically on Excel would be greatly appreciated