Ultra: Latin from ultra meaning beyond, from Latin ulter meaning situated beyond (more at ulerior....)
Violet: Middle English, from Middle French violete, diminutive of viole, from Latin viola (no relation to the viola, a musical instrument, which is Italian and Spanish in origin.)
Ultraviolet is "situated beyond the visible spectrum at its violet end."
I wonder how many of you remember walking into a head-shop and going into a black light lit back-room (now there's a tongue twister) that was papered with posters all glowing eerie colors; green-yellow, orange, blue-white.... White tshirts, fingernails, eyeballs, all fluoresced a ghostly violet. My friends and I liked to go into those rooms just to see how funny we looked. None of us were really interested in the posters. 1. They were too garish. 2. We would have needed to buy a black light and have a dark room in which to hang the posters. 3. We'd rather have spent our money on albums.
I know you're wondering. How am I going to relate ultraviolet light to writing?
It's like this. Sometimes the characters in books or stories appear or seem to be one thing, but when a black light is focused on them...well, ghostly traces of flaws or dreams or fears show up.
Readers tend to walk into a normal looking room. It's the writer's job to turn on the black light. But beware. Too much and the character turns into an fluorescent imitation of Elvis. Too little and the character is a stick figure.