The only references I can find dealing with the trousers are those of 1872, when the Army introduced white, un-trimmed trousers for wear in hot climates during the summer - though extent of use varied over time.
These were worn up to the 1890s.
The Army generally didn't describe enlisted work uniforms in Regulations, because fatigue or work uniforms were: (1) issued to the men, (2) were well known to Army members, and (3) the manner in which the uniforms were worn was not of much concern to Officers.
The general practice of little or no information continued until after WWII, when Uniform Regulations became more voluminous, and the fatigue uniform became worn more in public, and thus the uniforms' appearance became a point of interest for Commanders.
Now if you want to know more about the Khaki/Tan stable frocks and such - that's a different topic, and I have information on that uniform as well.
That was a light brown canvas uniform - often made from salvaged shelter halves - and canvas can get somewhat warm...
Vaya,
Scouts Out!