change button colour when clicked

Hello people

This follows on from a previous post about changing the text in a button when clicked, my code now looks like this:

Sub Button16_Click()

    Dim strCap As String

    With Columns("M:R").EntireColumn
        .Hidden = Not .Hidden
        If .Hidden Then
            strCap = "Show R&R"
        Else
            strCap = "Hide R&R"
        End If
    End With

ActiveSheet.Buttons(Application.Caller).Caption = strCap

End Sub

What I want to now do is change the colour of the button to green when it displays the 'Hide R&R' option (when it says 'Show R&R' the colour can stay the same standard grey). How do I do this? Can anyone help please?

Thanks
Kenny