The "Red Shoulders" constituted a group of B1-series battle droids answering to General Grievous. These droids featured shoulders painted red, enhanced sensor programming, and the capability to rotate their heads and waists a full 360 degrees.
Originally, the "Red Shoulders" were planned for inclusion in the canon animated series Star Wars: The Clone Wars, but their appearance was eventually removed from the show.
It's highly probable that the "Red Shoulders" were an homage to the Gilgamesh Space Force 10th Division 24th Melkian Strategic Armored Trooper Special Operations Corps Unit X-1, which gained widespread recognition as the "Red Shoulder Battalion" or simply "Red Shoulders." This unit featured prominently in the dark and realistic 1983 military science fiction anime Armored Trooper VOTOMS. The Red Shoulders, of which the series' main character was previously a member, were an elite division of Armored Trooper soldiers, known for their exceptional precision and utter lack of concern for human lives, regardless of civilian status. Members of Unit X-1 distinguished themselves by painting the right shoulder armor of their Armored Trooper mecha in red.