Liches are permanently stuck in the clothes they turned into liches in, that’s canon. So Lydia and Edward were in dark robes, and Lup and Barry were wearing their full hooded IPRE ones. It was dawn when they did the ceremony, maybe it was chilly. Maybe they just wanted to really commit to the lich aesthetic.
But, like, imagine if they’d been wearing crop tops, or if they’d gone through it in matching double denim. What if on a whim Lup suggested they cut holes in sheets and turn into liches while looking like some classic cheap ghosts. Psychological warfare, everyone’s afraid of a charmingly floral patterned specter right out of your Halloween daydreams.
“Well, we call them the red robes. In reality, it’s possible you might need to look out for them in other forms as well…. ah, we have records of liches in coordinating pajamas. If you see them, just run.”