I guess I should have checked my own book "Lee's Tigers" before replying the first time. One company in the 7th Louisiana was the Virginia Blues. It was 80% Irish and might have worn blue uniforms judging from the name. One member of the regiment said the men wore pieces of red flannel on their arms to identify themselves in the battle at Blackburn's Ford on July 18, 1861, but he doesn't mention them doing it on July 21 at Bull Run. He referred to the Blackburn's Ford fight as the "Battle of Bull Run," so that might be confusing things somewhat.