This figure put me in the mood for some US Cavalry movies, so I decided to start with the four John Ford/John Wayne classics:
Fort Apache (1948)
She Wore a Yellow Ribbon (1949)
Rio Grande (1950)
The Horse Soldiers (1959)
Watching Fort Apache immediately got me thinking about the yellow cavalry stripes on the trousers. In Ford's movies they're wide and prominent on all NCOs and officers. On Dunbar they're very narrow.
The regulations from 1861 are found in this Wikipedia entry:
https://en.wikipedia.org/wiki/Uniforms_of_the_Union_Army#cite_ref-8
Privates had no stripes at all, which John Ford got correct.
DID have it correct on Dunbar as a pinstripe - I don't know why the regulations referred to it as a "welt", as the modern definition of a "welt" with regards to trousers "is a strip of fabric used to cover or bind one or both edges of a pocket opening."
EDIT:
After I hit post something else turned up, referring to M1876/84 NCO & Officer Cavalry Trousers. The regulations were apparently reversed some time after the Civil War:
It would make sense as I'd previously been reading this:
JOHN FORD'S CAVALRY TRILOGY: MYTH OR REALITY?
A thesis presented to the Faculty of the U.S. Army Command and General Staff College in partial fulfillment of the requirements for the degree
MASTER OF MILITARY ART AND SCIENCE
by JEFFREY C. PRATER, MAJ, USAF
B.S., United States Air Force Academy, 1975
Fort Leavenworth, Kansas 1989
The only fault they picked up on was that the stripes were the same width for all NCOs and officers: