Rect rec = new Rect (0, 0, Screen.width, Screen.height/4);

so I’d want something like rec.ColorFill(Orange)

anyone know a way to achieve something like this?

In your favorite image editing program, create a white texture. It does not have to be very big. Then you can do:

void OnGUI() {
    GUI.color = Color.red;
    GUI.DrawTexture(rec, tex);
}

Where ‘tex’ is a reference to your texture. Note the rec is in GUI coordinates. If your rec is in Screen coordinates, you’ll need to the following:

rec.y = Screen.height - rec.y;