“Fun fact: The costume department went above and beyond the call of duty in “Legion.” For a superhero show firmly grounded in reality, subtle alterations to classic looks provide an anomalous vibe without feeling cartoonish… the orange uniforms patients sported in the mental hospital actually contained a secret code for the staff to distinguish which inmates were the most dangerous.
A white stripe down the sleeve signified the lowest risk. They were calm, relatively safe individuals — like Syd. Patients with a yellow stripe are somewhere in the middle: a risk, but not a consistent threat. David wore a yellow stripe, but only because the doctors didn’t fully realize his powers (until it was too late). Lenny, however, sported the most dangerous marking: a red stripe. She was just too rambunctious for the staff to ever fully trust. (After David and Syd switch bodies later in the episode, you can hear Lenny trying to calm hospital security who are restraining David by saying, “He’s in the yellow,” meaning, “He’s not violent. Take it easy.”)”