You seem to like to contridict yourself.
I am sure you would be quite aware that the part you are looking at is called a filler pass. The weld underneath this is called the root pass which is what gives you the strength and seal. The reason you don’t see the heat coloring is due to the fact we wire brush everything so that when the manifold is heat cycled you do not see the discoloring.
The rest of the welding on the exhaust was done with a MIG welder.
Adrian