It is not possible to directly access the colour of a cell in an Excel worksheet. Thus you can not write an expression such as “if the cell is red, do this”. However, it is possible to use a small amount of VBA to generate a “custom function”, which you can then use to do precisely this.
Bring up the VBA Window by pressing the <ALT> and <F11> keys.
Select your file from the list on the left (if it isn’t already selected) and click on the Insert Menu and choose “module”. Excel will display a blank white space to the right.
Into this area, copy the code below, from Sub to End Sub inclusive.
Function getRGB(rcell) As String
'allows excel to determine the colour of a cell and return the RGB value.
Dim C As Long
Dim R As Long
Dim G As Long
Dim b As Long
C = rcell.Interior.Color
R = C Mod 256
G = C \ 256 Mod 256
b = C \ 65536 Mod 256
getRGB = "RGB(" & R & "," & G & "," & b & ")"
Now you can call this custom function into any cell in your sheet by entering
=getRGB(A1) to pull the RGB code into the worksheet.