The pictures aren't from the right perspective for me to tell if you have a natural gas or a propane burner. The air orifices shown in the pictures are the same size for natural gas and propane. Take a picture down the burner tip so I can see the size of the gas orifice relative to the burner tip.I tried a few perspectives, but guess I missed the important one I'll try to get you the picture you want.
What if I said it burns orange no matter how low the propane is turned?
If the entire flame is orange than it is a natural gas burner. If only the tip of the flame is orange than it probably is propane. Still a picture would be helpful to confirm.