Good Omens (1990) is a wacky-wry fantasy novel by Neil Gaiman and Terry Pratchett. One of my favorite scenes occurs in Chapter "Thursday" as Adam, a boy of apocalyptic importance, is visiting Anathema Device, a "Practical Occultist" (aka witch):
She stared at Adam. There was something odd about him, but she couldn't put her finger on it. ...
and a few pages later:
... She was still trying to put her finger on what was so odd about Adam, and then she realized what it was.
He had no aura.
She was quite an expert on auras. She could see them, if she stared hard enough. They were a little glow of light around people's heads, and according to a book she'd read the color told you things about their health and general well-being. Everyone had one. In mean-minded, closed-in people they were a faint, trembling outline, whereas expansive and creative people might have one extending several inches from the body.
She'd never heard of anyone without one, but she couldn't see one around Adam at all. Yet he seemed cheerful, enthusiastic, and as well-balanced as a gyroscope.
but by the next page it is revealed:
It might, or might not, have helped Anathema get a clear view of things if she'd been allowed to spot the very obvious reason why she couldn't see Adam's aura.
It was for the same reason that people in Trafalgar Square can't see England.