1860's US Cavalry Uniform Color Question

Having only seen the uniforms in colorized John Wayne movies, is the blue a dark navy? tried a royal blue and that was way too bright.

Brand new...a very dark blue. It would sometimes even appear
"darker" than the black leather equipment. This would undoubtedly change, due to the "elements". Also, individual taste in clothing would result in a lot of leeway, and variation.

Later on, even dark gray wool shirts were issued, and these were often worn in lieu of the "regulation" blue shirts/coats.

One thing to avoid...the "yellow scarf". This was mostly a
"Hollywood" thing, made popular by John Ford (also by F-Troop...lol).

Neckerchiefs were worn, as a practical item, but there was really no
"standard" color or pattern.

So, the coat could be very dark blue; or a very dusty and faded blue.
If you avoid an "electric blue", you will be okay.