That is some good brush work, especially if you've only been painting for a few weeks.
The vivid blue coats & hats are painted very well - & they would be the source for any minor criticisms anyone would have. The minor criticisms would come only from those who would insist on historically accurate colors.
Dusters were white, light gray, light tan or an off-white. They were worn to help keep cloths clean & worn by some outlaws & lawmen because they could conceal a long gun.
Slickers were another long coat worn that were rubberized to keep clothes dry. Slickers were brown, tan, or yellow.
Frock coats came in a variety of colors with black, dark blue & gray being the most common.
The 1880s, 1890s & the early 20th century saw an explosion of color as chemical companies were creating new dyes and more expensive clothing would have been dyed with dyes that held their color longer - more colorfast.
It would not be unusual to see a cowboy in a pink shirt - the shirt may have been intentionally dyed pink or it may have begun as a red shirt that faded over time.
Anyway, the only criticism you would have would be some button counter saying "Pinkertons didn't wear blue" - don't let them get to you - they look great.