BmpBitmapEncoder Background is alway black

i am converting the multiple children of an inkcanvas to a flattened bitmap. But when i create it, it puts in a black background no matter what. I just want it to have a white background... here is my code if anyone has any pointers i would really appreciate it. thanks

Code:

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ink1.Background = Brushes.White
            Dim rtb As New RenderTargetBitmap(675, 624, 96D, 96D, PixelFormats.Default)
            rtb.Render(ink1.Children.Item(0))
            For i As Int32 = 0 To gridcontent.Children.Count - 1
                If gridcontent.Children.Item(i).GetType.FullName = GetType(Button).FullName Then
                    rtb.Render(gridcontent.Children.Item(i))
                End If
            Next i
            Dim encoder As New BmpBitmapEncoder
            encoder.Frames.Add(BitmapFrame.Create(rtb))
            Dim fs As FileStream = File.Open(My.Computer.FileSystem.SpecialDirectories.MyDocuments & "\AssessmentImages" & "\Report" & ".bmp", FileMode.Create)
            encoder.Save(fs)
            fs.Close()

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ink1 is my inkcanvas, obviously.