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Detail of the thrust chamber wall.

There are two discolored spots, one on the top of the combustion chamber wall and one in the lower right of the injector. I'm not certain why the combustion chamber wall is that color, but area on the injector probably represents a clean spot, as other injectors are a brilliant copper color.

The area closest to the injector where the tubes change color are where the regenerative cooling tubes comprising the thrust chamber assembly bifurcate, or split in two. I'm uncertain as to why the tubes change color again closer to the exit plane.

Note the gaps in the interface between the thrust chamber and the nozzle extension; some of the relatively low-temperature gasses from the turbine exhaust manifold are dispersed through these gaps, providing film cooling for the nozzle extension.