I stand corrected. However, Gibb’s record is somewhat strange. His CSR cards record him as Corporal then Color Sergeant until a card dated after his death recording the rank of Ensign.

His picture in the book noted below and in Lindsley’s Military Annals of Tennessee show him as a Lieutenant

Robert H. Gibbs was appointed standard-bearer of the regiment during the reorganization of the army at Corinth in 1862. At Perryville was killed after having placed the colors on of the the guns of the enemy battery. p. 55
His picture on p. 56 listing rank of Ensign and what appears to be the single bar insignia of a Lieutenant on his colar.

True Tales of Tipton County Tennessee By Gaylon Neil Beasley
http://books.google.co.uk/books?id=lLmHt8LUFfcC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false