Perception, Not Magic
We all experience "auras" unconsciously. When you stand too close to someone in an elevator, you feel uncomfortable because their field (presence) is impinging on yours. When someone walks into a room and "fills it" with charisma or anger, that is an effect of their projection.
Historically, sensitive practitioners developed language to describe these subjective feelings of density, color, or texture. These were attempts to categorize biological and psychological signals, not necessarily to describe a literal visible light spectrum.