Not much protection from this method. Flame coloring changes the structure of a very thin oxide layer to alter the refractive index of the material so that the light reflected is chromatically shifted. Conversion treatments like nitre bluing, rust bluing, or parkerizing can stave off rust, but still need oiling to complete the barrier. Plating is still the best for corrosion, but there's plenty of stainless available to us if you really want to defer maintenance as far as possible.