The Army originally intended canvas clothing for soldiers doing fatigue duty, since canvas was easier to clean than wool clothing. 

However, the cloth was found to be so comfortable by enlisted men, that officer's soon started having enlisted blouses modified for their needs. Although called "Brown" in the US Regulations, historians agree there were many shades of brown canvas used during this time frame, from a chocolate brown to a tan. 

As again, color variation was experienced from dye lot to dye lot, and the fabric tended to fade.