Here are three different variants of Colt Flat Dark Earth (FDE) in my reference collection.

Top example is a cerakote carbine upper receiver from around 2017.

Middle example is an anodized LE6940 upper receiver from a limited production run of about 1500 examples. Estimated time frame is 2011/2013. Note the bronze tone in the color.

Bottom example is an anodized prototype IAR6940 upper receiver from around 2008/2009 time frame.