Calculate the color of GDI hpalette - GDI+ secrets

    Private Function GetHppaletteColor() As Color
        Return Image.FromHbitmap(New Bitmap(Me.Width, Me.Height).GetHbitmap(), IntPtr.Zero).GetPixel(0, 0)
    End Function

or

  Private Function GetHppaletteColor() As Color
        Return Image.FromHbitmap(New Bitmap(Me.Width, Me.Height).GetHbitmap(), Graphics.FromHwnd(IntPtr.Zero).GetHdc).GetPixel(0, 0)
    End Function

the below code shows hoe to save the screen bitmap which hold the hpalette color

        Dim rect As Rectangle = CType(Nothing, Rectangle)
        Dim devices As Screen() = Screen.AllScreens
        For i As Integer = 0 To devices.Length - 1
            Dim device As Screen = devices(i)
            rect = Rectangle.Union(rect, device.Bounds)
        Next

        Dim mask As Bitmap = Image.FromHbitmap(New Bitmap(rect.Size.Width, rect.Size.Height).GetHbitmap(), Graphics.FromHwnd(IntPtr.Zero).GetHdc())

        Dim fileName As String = Application.StartupPath & "\screen.jpg"
        mask.Save(fileName)

' Test Control

Public Class DominantControl
    Inherits Control

    Public Sub New()
        MyBase.SetStyle(ControlStyles.ResizeRedraw, True)
    End Sub

    Protected Overrides Sub OnPaintBackground(pevent As PaintEventArgs)
        Dim rect As Rectangle = New Rectangle(0, 0, MyBase.Width, MyBase.Height)
        Using sb As New SolidBrush(GetHppaletteColor())
            pevent.Graphics.FillRectangle(sb, rect)
        End Using
    End Sub

    Private Function GetHppaletteColor() As Color
        Dim rect As Rectangle = CType(Nothing, Rectangle)
        Dim devices As Screen() = Screen.AllScreens
        For i As Integer = 0 To devices.Length - 1
            Dim device As Screen = devices(i)
            rect = Rectangle.Union(rect, device.Bounds)
        Next
        Return Image.FromHbitmap(New Bitmap(rect.Width, rect.Height).GetHbitmap(), Graphics.FromHwnd(IntPtr.Zero).GetHdc).GetPixel(0, 0)
    End Function

End Class

build the control, add to form and notice what will happen when you try to change the control backcolor

Reference