"Graybacks" was the common name for Body Lice.
Edit - I am only going to accept lice, or body lice, as a correct answer to this question.
Some players answered that "Graybacks" was a term referring to Confederate paper money. Others answered that "Graybacks" was a term referring to Confederate soldiers.
My ruling, based on the wording of the question and the title of the thread, is that neither of these is a correct answer.
The question asked who (not what) did both Northern and Southern (that's both Northern and Southern) soldiers call the "graybacks." The title of the thread was "Gross." Players are reminded that, while it is not always the case, sometimes the title of the thread is a clue to the desired answer.
Although it is true that Confederate paper money was called graybacks, it was a thing, not a living creature, so it is not an appropriate answer to a question that begins with "Who." There was nothing particularly gross about the paper money, either.
And although it is true that Confederate soldiers were called graybacks, according to what I can find, the term was used by the Northern soldiers exclusively, as a mark of disrespect for the Confederates. I can't find any indication that the Southern soldiers referred to themselves with this term.
I suppose "gross" might be an apt description of a Confederate soldier with lice, but if the Northern soldiers were honest with themselves, they would have to admit it was an equally apt description of a good many of them.
Hoosier
Bringing the