Question

How can I set the background color for a form as specified in the attached image?

Answer 1

One way would be to directly use the image as the form’s BackgroundImage.

If you want to achieve this proceduarally (more flexible), you can manually paint the form’s background using OnPaintBackground:

protected override void OnPaintBackground(PaintEventArgs e)
{
    using (var brush = new LinearGradientBrush
               (DisplayRectangle, Color.Black, Color.DarkGray, LinearGradientMode.Vertical))
    {
        e.Graphics.FillRectangle(brush, DisplayRectangle);
    }
}

protected override void OnResize(EventArgs e)
{
    base.OnResize(e);
    Invalidate(); // Force repainting on resize
}

Result: