I know the early Wisconsin regiments where issued gray uniforms.
But it was not only an early war issue.
Another was the fact that some CSA eastern troops was issued uniforms that was made from british wool and they where a grey-blueish color.
So when Longstreet went west i late 63 his blueclad men caused confusion both in battle and during more peaceful times. This Include Grant who mention in his memoirs that he during an inspection of his picket line he had a chat with one of Longstreets men... and the rebs called out their guards for him... showed their respect and he rode back.
Grant write "General Longstreet's corps was stationed there at the time, and wore blue of a little different shade from our uniform, Seeing a soldier in blue on this log, I rode up to him, commenced conversing with him, and asked whose corps he belonged to. He was very polite, and, touching his hat to me, said he belonged to General Longstreet's corps. I asked him a few questions - but none with a view of gaining any particular information - all of which he answered, and I rode off."
Found at the end of chapter 41.
(imagine a US soldier today just having a chat with an very high ranking enemy commander and letting him go?)