Auto Recalculate instead of pressing F9

Hi All,

I've the below codes and every time i need to press F9 to recalculate it.. is there any code to add in the module to recalculate automatically when value changes.

Function CountColour(rng As Range, clr As Range)
Application.Volatile
Dim c As Range
For Each c In rng
    If c.Font.Color = clr.Font.Color Then
        CountColour = CountColour + 1
    End If
Next
End Function

I tried some of the codes and it doesn't work..