I have been watching Ken Burns’s 9-episode “Civil War.” In one of the episodes, the narrator said that the Confederate soldiers wore “grey and butternut” and the Union soldiers wore “blue.” In reality, it was a little less clearcut as captured by these two drawings, originally in Harper’s Weekly, August 17, 1861 (page 520-521). (Source: NY State Library)
While Confederate officers and some soldiers wore grey, most of the clothing was homemade. The South had few factories of any kind; it was the North that was home to textile factories. Further, the war cut off trade between the North and the South, and the North blockaded the southern ports. Thus obtaining dye stuffs (e.g., to get a “real” grey) was increasingly unlikely.
Thus, Southerners, especially, had to make their own uniforms. The most common dye made by ordinary folks came from the shell of the fruit of the North American walnut tree (Juglans cinerea). The resultant color on protein fibers was a sort of brownish; on cellulose fibers it would have been a different brownish color. Sometimes vinegar was used as a mordant the protein fibers; if not used, the color would tend to run when subjected to moisture (e.g., rain or sweat). This dye bath could be made quickly, was not toxic and dyed quickly.
All-in-all, given the time period (1861-1865), keeping to a strict color-coordinated uniform would have been problematic. Simply, soldiers wore what they had (often brown or tannish color), what their women sent them off to war with, or what they could scavenge.
While Confederate soldiers were commonly called “greybacks” and “butternuts,” I have a hunch that given the long marches through fields, slogging through mud and rain, wearing their clothes every hour of every day, and the lack of clean clothes, no matter what color clothes worn, no matter what the uniform started out looking like, all the uniforms looked sort of muddy brown-grey.