Are you looking for colors used by ranchers, farmers, soldiers on/off duty, merchants and other townfolk, Native Americans, Hispanics, or so on?
You'll want to use plenty of blues, particularly dark blues. Brown canvas/cotton was popular. Non-fatigue/work clothes would consist of brown or gray or dark gray or dark blue or black coats and/or waistcoats and trousers and lighter-colored shirts, at least for those who didn't do physical labor. Flannel was popular, particularly red and blue flannel. Any color was possible, it just depended on how the goods (dyes, cloth, manufactured clothing, etc) made it to town; before the railroad, fancy items would be limited to the wealthier, but towns close to railroad stations or established trails like the Santa Fe Trail would have greater diversity of clothing colors and designs. For the most part just think of colors used today, toned down a little; hot pink obviously would not be worn, but dresses would be of a variety of colors, and cotton or wool-based clothing would be mostly of simple colors and designs.