I have seen a lighter area at the forte of a blade on a Chinese dao that Philip Tom attributed to annealing. The idea was to reheat the base of the blade and let it cool slowly to increase durability at the expense of hardness in an area where hardness is not as important. This is not a comment on the underlying pattern of the steel, but the lighter area at the base of the blade looks almost exactly like what I saw on the dao.
Josh
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