Try this to start
Sub TurnGreen()
Dim myRng As Range
Dim newRng As Range
Dim c As Range
Set myRng = Range("C7:AH72")
Set newRng = myRng.SpecialCells(xlCellTypeBlanks)
With newRng
.Interior.ColorIndex = 4
End With
End Sub
and to reverse
Sub ReverseGreen()
Dim myRng As Range
Dim newRng As Range
Dim c As Range
Set myRng = Range("C7:AH72")
Set newRng = myRng.SpecialCells(xlCellTypeBlanks)
With newRng
If .Interior.ColorIndex = 4 Then
.Interior.ColorIndex = xlColorIndexNone
End If
End With
End Sub
HTH
Regards
EDIT : Amended ranges