Headcanon that before the sides were fully developed and able to design their own outfits or control things about their appearance fully, a lot of it was just decided by the mind because of tropes or what Thomas thought of them.
Like because Thomas didn’t fully know hoe wearing glasses worked, for a while if Right Brain and Left Brain took off their glasses they’d go from complete vision normally to completely blind and unable to see anything instantly. It only changed after Thomas was shown a video about how eyesight issues worked in late middle school that it changed.
And also because Vision, Right Brain, and Left Brain only had stable appearances when Thomas was a teenager because only Thomas knew them. Meaning Janus, Virgil and Remus fully just couldn’t control their appearance or what they looked like. Janus and Virgil didn’t look like anything, but because Remus was Roman’s ‘identical twin’ and most of the time that trope means identical in every way, Remus just looked exactly like Roman in every way, even down to clothing. Very uncanny valley if you ran into him because he sounds like Roman, looks like Roman, and dresses like him, but just isn’t.
Because evil snakes always hiss in movies, Janus would compulsively hiss if he wasn’t talking or eating or doing anything else with his mouth. He had to really focus to make it stop.
