The PictureBox's Paint event handler makes a LinearGradientBrush. The rectangle the gradient covers is slightly larger than the PictureBox's client rectangle. The brush uses the angle m_Theta to determine the gradient's angle.

The program fills the PictureBox with the brush. It then updates m_Theta so the gradient rotates next time.

Finally the program draws some text over the colored background.

Private m_Theta As Single = 0
Private m_Delta As Single = 10

Private Sub tmrRotate_Tick(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles tmrRotate.Tick
    picCanvas.Invalidate()
End Sub

Private Sub picCanvas_Paint(ByVal sender As Object, ByVal e _
    As System.Windows.Forms.PaintEventArgs) Handles _
    picCanvas.Paint
    Dim rect As New Rectangle(-3, -3, _
        picCanvas.ClientSize.Width + 6, _
        picCanvas.ClientSize.Height + 6)
    Dim br As New LinearGradientBrush(rect, Color.Red, _
        Color.Blue, m_Theta)
    e.Graphics.Clear(picCanvas.BackColor)
    e.Graphics.FillRectangle(br, Me.ClientRectangle)
    br.Dispose()
    m_Theta += m_Delta

    Dim string_format As New StringFormat
    string_format.Alignment = StringAlignment.Center
    string_format.LineAlignment = StringAlignment.Center
    e.Graphics.DrawString("Some Text", Me.Font, _
        Brushes.Black, _
        picCanvas.ClientSize.Width \ 2, _
        picCanvas.ClientSize.Height \ 2, _
        string_format)
End Sub