Hi , My Question is , in rendering fixed pipeline we can indicate each vertex color , for example : <code> vert[0].Color=(int)Color.Red.ToArgb(); vert[1].Color=(int)Color.Green.ToArgb(); vert[2].Color=(int)Color.Blue.ToArgb(); </code> Is there any way to write a VertexShader that Output three different diffuse color ? Thanks in advance ..

A vertex shader will only operate on a single vertex at a time. If you need a shader to operate on primitives, look into geometry shaders.