Not actually an oxymoron. It's the color past ultra-violet. The technical term for it is infra-black. It can be seen quite easily under experimental conditions.
To perform the dark light experiment simply select a healthy brick wall with a good runup, and, lowering your head, charge. The color that flashes in bursts behind your eyes, behind the pain, just before you die, is infra-black.
a fairly dark version of light
"that's some pretty dark light, man."