The world of the spirit begins where logic ends. Logic is limited by the boundaries of reason, which is further limited by the limitations of the individual's buddhi.
However, since most speak and comprehend only the tongue of logic, we can try to understand the aura which is of the spiritual realm. All bodies emit heat radiation or vibrations. With non-living bodies, since there is no immediate change in their structure, this emission remains constant. In living bodies cells are constantly being destroyed and created; the rate of vibrations are continuously changing. This is the superficial or logical explanation of what auras are and why they are constant or changing.
A lot of 'scientific' study of physical auras has been done in the West in recent years. Researchers have variously called it the human atmosphere, force field, and bio-energy. The fundamental substance of aura is best described by the Sanskrit term, prana. For our present purposes we could understand it as the vital essence or force, which is the basis of all manifested life. It is the steam that runs the physical and mental machinery of life. The colours of our mental states are manifested in the pranic substance of our auras.
Logically, these colours are regulated at seven energy centres of the body called the chakras. Each of the chakras, mooladhar, swadhishthan, manipoorak, anahat, vishuddhi, ajna and sahastrar vibrate at a particular colour frequency. It is like software for each chakra. When the software malfunctions or the wrong software goes into the wrong chakra, imbalance and malfunctioning occurs. Any imbalance that stays for too long becomes chronic and manifests as an ailment in the physical body.
What the clairvoyant can see are the aura or chakra imbalances in the shade of the colour being too dark or heavy or colours other than the chakra's own colour manifesting. Considerations like what shade is mixing with the natural colour, in what proportion, the positioning, the luminosity. All determine the state of the being. Only an enlightened person would be able to interpret the infinite permutations and combinations correctly.
The real person stands revealed once you have the correct interpretation of the auras. You can hide your face by applying make-up or you may hide your true body by wearing loose fitting clothes, you may even lie about your character and intention but it is impossible to hide your true self from the eyes of a clairvoyant, for aura is something you cannot hide.
The entire spectrum of colour and light are in human auras. Different colours belong to different areas around the body. Lower centres or chakras of the body are associated with darker and heavier colours like reds and browns. The higher centres have light pink, violet and blue. Again, more evolved souls have much more luminescence in their auras than the average individual.
What does your aura tell you? Your aura indicates your state of health to come, specific diseases that are manifested or are going to manifest in your body, your mental and emotional state, your level of intelligence, and how evolved you are as an individual. Assigning meanings to specific colours is of no use to the novice. The positioning, thickness, luminescence, shade and changeability are some of the factors that are taken into account in interpretation. The interpretation is always left to the guru.