In 1989, Barbara Bowers, Ph.D. published What Color Is Your Aura : Personality Spectrums for Understanding and Growth, describing the fourteen patterns of aura color. The aura is a reflection of mental, physical and emotional processes and is described as a luminous egg-shaped cloud of pulsating energy. The aura is multidimensional, having size, shape, texture, patterns and even sound for those gifted with ability to see them. These differing attributes combine to create a symbolic language which is the basis of the Personality Spectrum as formulated by Dr. Bowers.
The aura extends out from the human body in all directions about six feet. The size and clearness of color is modified by the spiritual, mental and emotional health and strength of the individual. The more in touch with our own unique talents, the stronger, clearer and richer the colors. The auric colors themselves appear to be innate and permanent, changing only in the face of a radical life shift or crisis, such as a near-death experience, or extraordinary psychological or physical trauma. However, some students of the aura (specifically Pamala Oslie in Life Colors) believe that the aura color is an early life choice and can be modified or overlaid by later choices and societal demands. In these instances, the earliest choice is considered the most valid and the later color overlays may be distorting the innate or initially chosen manifestations of the personality.
What bearing does this have on writing? Consistency A story dealing with psychic phenomena, or emphasizing metaphysical or meta-psychological plot points, describing a character who is firmly established as a rational, duty-driven individual as having an aura indicating he is a spiritually driven visionary/dreamer is inconsistent - unless you intend to show how this rational being is really an other-worldly poet under that hard exterior or has undergone a crisis leading him to become dreamer and poet - or vice versa.
Black Auras: While general consensus in the literature indicates that disease may be indicated by 'splotches' in the aura - fainter or less luminous areas or even grayed out areas - an aura that is completely missing or colored black is not likely in something alive as all living things emanate energy (and therefore an aura). However, in fiction, a black aura is often used as an indicator of a being using 'negative life energy', as in a vampire, a creature that ingests life energy in the form of living blood; or a being turned to the destruction of all life (ie. utterly evil).
Some books on the subject: Auras, Chakras, and Personality Colors