According to the book Auras, written by Edgar Cayce, the Aura reflects vibrations of the soul.
Follow up post from Comments – What is an Aura?

Here are some of the colors he speaks of and their basic meanings:

Reds- Force, Vigor, and Energy

Dark Reds- Temper, Nervous Turmoil

Pinks- Immaturity, Youth

Oranges- Thoughtfulness and Consideration

Yellows- Health and Well Being, Friendliness

Greens-Helpful, Strong and Healing

Blues- Spirit, Contemplation, Artistic

Violets-  Religious seekers

Whites- Perfect balance

Helpful hint for the eye to see an Aura.

Put on a t-shirt and go to a mirror in your home. Hold both arms up in a 90* degree angle.(bend your elbow) Keeping them locked in this position, raise them slowly up over your head. As you do this, look at yourself in the mirror. Paying attention to the angle (cornered part of the arm) and de-focus your eyes a little; like you do when you start starring off during a day dream. You should see an energy body following split seconds after the physical arm.

You may need to do this a few times before you get it.

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