I've ordered 4 "pearl gold" pieces of part 92690 on BrickLink. Unfortunately, the seller had to adjust the order as he only had 3 such pieces, he proposed adding two more in "flat dark gold" in exchange, which I agreed to.
However, searching the BrickLink database, no such piece exists in flat dark gold in any set (the seller acknowledged that and he has no other explanation).
These are the pieces (pearl gold on the left, flat dark gold on the right):
My question: What is the origin of the flat dark gold pieces? Is this discoloring because of age? Or is the BrickLink database in error? Note that, at the time of writing this, 70 sellers are offering this piece in flat dark gold.