To display "G" in Excel if a cell's fill color is green:

1. Select the cell where you want to display the "G" value (let's say it's cell E1234).
2. In the formula bar, type the following formula:
   
   
   Formula:

   =IF(D1234=CELL("color",D1234),"G","") 

3. Press Enter to apply the formula.

This formula checks if the fill color of cell D1234 is green. If it is, then it displays "G" in cell E1234. If it's not green, then it displays nothing (i.e., an empty string).

Note that this formula uses the function to check the fill color of cell D1234. The second argument of the function ("color") tells Excel to return the color of the cell. If the fill color of cell D1234 is green, then the function returns "G". Otherwise, it returns an empty string.