try this one.
Public Class Form1
Private WithEvents client As MdiClient
Private Sub Form1_Load(ByVal sender As Object, _
ByVal e As EventArgs) Handles MyBase.Load
Me.client = Me.Controls.OfType(Of MdiClient).First()
End Sub
Private Sub client_Paint(ByVal sender As Object, _
ByVal e As PaintEventArgs) Handles client.Paint
Using Brush As New Drawing2D.LinearGradientBrush(Me.client.Bounds, _
Color.FromArgb(0, 58, 140), _
Color.FromArgb(0, 215, 255), _
Drawing2D.LinearGradientMode.Vertical)
e.Graphics.FillRectangle(Brush, Me.client.Bounds)
End Using
End Sub
End Class