Pearl gold vs flat dark gold
There has been a slight change to the Pearl Gold/Warm Gold color recently that might explain the difference in color between those pieces. See this article on Reddit. Perhaps the right two “Flat Dark Gold” pieces are the newer recolor of Pearl Gold? I recall Jang from JangBricks talking about this as well in his videos.

Here is the picture from the Reddit article showing the new Pearl Gold on the top, and the old on the bottom.