Uniforms Federal issued black trousers.

major bill

Brev. Brig. Gen'l
Forum Host
Aug 25, 2012
Aa letter published in the Allegan Journal that had been written on July 7 1861 indicates that they were about to change their gray clothes for black, but the letter did not tell what type of back uniforms they were expecting to get. “We are to change our gray clothes for U.S. clothing this week; our new suits will be black.”https://civilwartalk.com/#_edn1

During this same time period the Federal government sent 3,000 pairs of black trousers to Michigan. I expect that these were issued to regiments forming in Michigan at that time. I am not certain how common black Federal issued trousers were.

https://civilwartalk.com/#_ednref1 “From the Third Michigan Regiment, Georgetown Heights D. C. Camp of Third Mich Regiment July 7th​ 1861, letter By G. W. Bailey”, Allegan Journal, July 15 1861, p. 2, col. 5.