[2005] optional parameters cannot have structure types

[jonwondering]

That's the error I get for this sig:

Public Sub DrawSphere(ByVal e As System.Windows.Forms.PaintEventArgs, _
                            ByVal X As Integer, _
                            ByVal Y As Integer, _
                            ByVal Width As Integer, _
                            ByVal Height As Integer, _
                            Optional ByVal Outline As Color = Color.DimGray, _
                            Optional ByVal ColorA As Color = Color.Black, _
                            Optional ByVal ColorB As Color = Color.Gray)

It's pointing to Color (in As Color = whatever). The weird thing is that I have not created a structure called Color. Any help?