The standard US blanket was gray with black end stripes. The letters US were sewn into the center of the blanket. That said there were many contracters who provided blankets to the US government during the CW. All were not alike but were similar to met the gov specs. Don't ever recollect reading about any that were blue although there were some bright red ones as well as browns and various shades between. There were enough of these blankets around at the end of the war and were probably used well past 1867. A search for CW blankets would probably provide more information.