Private purposeGuid As New Guid("12345678-9012-3456-7890-123456789012")
Private penValue As String = "pen"
Private highlighterValue As String = "highlighter"

' Add a property to each DrawingAttributes object to 
' specify its use.
Private Sub AssignDrawingAttributesInstrument()

    inkDA.AddPropertyData(purposeGuid, penValue)
    highlighterDA.AddPropertyData(purposeGuid, highlighterValue)

End Sub

' Change the color of the ink that on the InkCanvas that used the pen.
Private Sub ChangeColors_Click(ByVal sender As [Object], _
        ByVal e As RoutedEventArgs)

    Dim s As Stroke

    For Each s In inkCanvas1.Strokes
        If s.DrawingAttributes.ContainsPropertyData(purposeGuid) Then

            Dim data As Object = s.DrawingAttributes.GetPropertyData(purposeGuid)

            If TypeOf data Is String AndAlso CStr(data) = penValue Then
                s.DrawingAttributes.Color = Colors.Black
            End If

        End If
    Next s

End Sub