source: downloads/Samples/Media/materials/scripts/Hurt.material @ 5

/// Just a simple red quad blended over the scene
material RedQuad
{
    technique
    {
        pass
        {
            lighting on
            diffuse 0.0 0.0 0.0 0.5
            specular 0.0 0.0 0.0 1.0 
            ambient 0.0 0.0 0.0
            emissive 1.0 0.0 0.0
            cull_hardware none
            depth_check off
            scene_blend alpha_blend
        }
    }
}