The etheric is considered to extend two to four inches outlining the physical body - while the aura is much larger, measuring anywhere from about three to five feet in diameter, like an egg.
It is an energy field which is related to your spiritual energy as well as your state of mind. It is also said that disease will show up in the aura long before any onset of symptoms.
The quality of the energy field (aura) is expressed as a color. The aura is also related to the chakras - the chakras are said to generate the dominant hue of the aura.
When you can feel a person coming close to you, such as from around a corner, before you can see or hear them perhaps what you are actually feeling is their aura moving against yours.
Some people say that the aura contains every color in the rainbow; others say that most people have a "fixed" color that they tend to carry with them - others feel that the color of anyone’s aura changes constantly and that any view that you get of a person’s aura is merely the snapshot of their energy expression at the moment.
It is said that the reason why certain phrases like "she’s green with envy," or "he's a yellow coward," are part of the vernacular is because the ancients have always been familiar on some level with auras, their colors, and the energy behind them.
There is a type of photography that supposedly captures the colors in a person's aura - called Kirlian photography.