Can't use simple material alpha blending ?

Question

I want to make a simple quad (custom vertexs) fading in and out (work as a fade in/out background). I see there are some method to changing alpha , like vertex alpha , texture alpha , material alpha. But I want a simple changing alpha method by setting the material alpha , but somehow , I do not work. Below is my code : (DirectX 9.0 SDK 2004 Summer update + Visual Studio 2003) device.VertexFormat = CustomVertex.TransformedColoredTextured.Format; device.RenderState.AlphaBlendEnable = true; device.RenderState.SourceBlend = Blend.SourceAlpha; device.RenderState.DestinationBlend = Blend.InvSourceAlpha; backgroundColor = Color.FromArgb((int)backgroundAlpha * 0xff, 255, 255, 255); backgroundMaterial.Diffuse = backgroundColor; device.TextureState[0].AlphaArgument1 = TextureArgument.Diffuse; device.TextureState[0].AlphaOperation = TextureOperation.SelectArg1; device.Material = backgroundMaterial; device.SetStreamSource( 0, backgroundVertexBuffer, 0 ); device.DrawPrimitives( PrimitiveType.TriangleStrip, 0, 2 ); device.RenderState.AlphaBlendEnable = false; The alpha is control by backgroundAlpha ( 0 <= a <= 1). Anyone help ?