The aura is a field of energy surrounding a body. The aura is densest close to the source and becomes thinner moving away from it. The color, size, clarity and other characters of aura constantly change due to transition of physical, mental, emotional and ethereal state of being. Although aura is invisible to the physical vision most people can learn to "see" through practice.
Usage and study on this subject is related to color, chakra, and energy.
Warning: Read the following section at your own risk!
Aura colors and interpretation: