The human aura is an envelope of etheric energy surrounding the body. Etheric energy is pre-physical energy, more subtle than the electromagnetic energy which makes up physical matter. In the spirit realms, which you visit each night as your body sleeps, etheric energy can be plainly seen as a subtle light which illuminates the environment.
Etheric energy also makes up the subtle matter from which your astral or spirit body is composed. The aura reflects the thoughts and emotions of the person through colorations in its appearance. Dark, dense colors mean an absence of love and light. The light referred to here is etheric light, not physical light.
In a Universe filled with Love and Light, that are both available to everyone, the Universal flow passes through people EMPOWERING them as it passes and it will appear in its aura. It’s the same if someone has a secret agenda it will show up in its aura.
This act of restricting or stopping the natural flow of Love and Light produces a tell-tale appearance of darkness in the aura of that person.