They look similar to the originals but with a slight difference such has having white eyes. In the outer world, Cooper's doppelganger had black irises instead. The evolution of the arm's doppelganger had a yellow "head" instead of the white-colored original.
Behind the scenes Edit
The only times the word is used in the franchise, it is written "doppelganger" without umlauts, but in other fiction and folklore it is written "doppelgänger".
A doppelgänger is a paranormal double of a living person, typically representing evil or misfortune. In modern vernacular, it is simply any double or look-alike of a person, as is the original German meaning of the word.