I know that American soldiers wore blue uniforms from the Revolutionary War all the way up to the Spanish American War, but then at one point between then and World War I they switched to brown. Why did this change occur? Was it for camouflage? I know that in the War of 1812 and Indian Wars a lot of soldiers wore furs instead, and in the Civil War some soldiers wore ordinary clothes because there weren't enough uniforms, but why did they officially change the color of the uniforms?
This is an excerpt from an earlier answer I gave here
The Army adopted various kinds of khaki-colored uniforms before the Spanish-American War, (May 1898) but none were issued to troops before the campaign kicked off. The following American experience in the Spanish-American War showed that the blue color was definitely not suited for the modern battlefield of bolt-action rifles and fast-firing artillery with new powerful explosives, all using smokeless powder that improved visibility on the battlefield. Certainly, the development of the airplane and the military use of balloons and airships must have accelerated this process; the bright blue is easily spotted from the air against a background of grass or mud. Ornate hats with feathers, horsehair and other frilly accoutrements were also abandoned as unsuited for the modern battlefield.
The heavy blue wool uniforms (the same color had been in use in various forms since the Civil War!) that were used in the Spanish-American War were phased out completely by the end of the first decade of the 1900s; (undoubtedly taking inspiration from the British, who had decided to modernize their uniforms around the same time) the blue wool uniforms were replaced with a lighter cotton four-pocket coat and trousers with various other pieces of equipment that were dyed a dark tan or brown color. The color was changed to a more green drab before World War I due to the decision that tan was too light a color for jungle fighting.
Sources:
Survey of U.S. Army Uniforms, Weapons, and Accoutrements, by David Cole