Auto Color Cells

Many users of Excel have made it common practice to color code cells to help identify inputs, formulas, etc. For example, it is common to color all cells act as hard coded inputs (i.e. not a formula) blue, all formulas black. This Excel macro looks at the contents of each selected cell and sets the color appropriately. Further I have added the green coloring for all external references.

' Set the color of cells to blue or black respectively
' Copyright under GPL by Mark Grimes
' Keyboard Shortcut: Crtl+Shift+C

Sub mgSetColor()
    For Each c In Selection.Cells
        If Left(c.Formula, 1) = "=" Then
            If InStr(c.Formula, ".xls") Or InStr(c.Formula, ".XLS") Then
                c.Font.ColorIndex = 10
            ElseIf InStr(c.Formula, "OFFSET") Then
                c.Font.ColorIndex = 9
            Else
                allNumbers = True
                For i = 1 To Len(c.Formula) - 1
                    If (Asc(Mid(c.Formula, i, 1)) < 40) Or (Asc(Mid(c.Formula, i, 1)) > 61) Then
                        ' MsgBox "Setting false: " &amp; Mid(c.Formula, i, 0) &amp; " = " &amp; Asc(Mid(c.Formula, i, 1))
                        allNumbers = False
                        Exit For
                    Else
                        ' MsgBox Mid(c.Formula, i, 1) &amp; " = " &amp; Asc(Mid(c.Formula, i, 1))
                    End If
                Next
                If allNumbers Then
                    c.Font.ColorIndex = 5   ' blue
                Else
                    c.Font.ColorIndex = 0   ' auto
                End If
            End If
        Else
            c.Font.ColorIndex = 5
        End If
    Next
End Sub