The perception of auras is a kind of synesthesia (emotions => vision). It can also be related to optical illusions (like contrast amplification).

Spontaneous synesthetic aura perception is very rare, and I don't know if you can develop it later on, or if secondary "aura readers" percieve the second kind, or if a strong emotion can trigger the phenomenon is someone who usually doesn't percieve it.

There's nothing magical related to that.