There are energy patterns in and around the body are a bit more rigid than the random energy floating around. This is what a lot of energy folk call the aura.
I know, I know. I was loathe to admit such things, but when I started seeing it I had to give in. There's a lot of crap going around in the New Age community, but the aura, in my experience and almost all of the other energy workers I know, feel it's there. But some of the loud voices in this community get funny ideas (mostly generalizations based on only associating with limited sets of people with similar beliefs) about structure and color.
For example, While I find that "aura reading"

Well, not really. It's a snapshot, and is changing all the time. If you watch an aura over time (which is not easy to do, even for those of us lucky to see the blasted thing in the first place) you can see what parts are stable and what parts change... well, you can figure out a lot about that person. it's not like mind reading, since you don't know *why* someone is feeling hostile or uncomfortable, or happy and thinking deep thoughts or feeling close to spiritual things, but you know they are there at that moment or a moment or two before. It's also sometimes hard to tell the difference between say, eddies created by recurring thought patterns and say, a long lasting injury. Possibly it's because I've lapsed on my enlightenment subscription.

It's hard for me to go on at great length about the aura without mentioning the chakras, which are wheels of light or flowers of light or portals or gems or however you visualize these zones of the energy body that regulate and pool energy. They are the organs of your aura, so to speak. One of the things that almost no one talks about is how different people have different kinds of auras and sometimes even chakra arrangements. Yes, most people have the standard 7 in the standard colors, but just because they don't doesn't mean that they are automatically unhealthy or broken. Shaman types, or people with idiosyncratic belief systems or physical differences or alternative sexualities don't always play by the same rules on an energy level. And, this doesn't mean they are bad, it just means that you may not be in tune with how they do things, so it may seem... dissonant or disorienting. This is basically a cue that you may not want to share energy with them right away, at least until you understand how their energy field actually works, or doesn't work as the case may be. Just because it makes you uncomfortable, doesn't mean it's wrong and needs to be fixed. Also, remember that what colors mean for you may not be true for someone else. So the next time you feel that person with a big black aura might be out to eat your soul... consider that black is also used by some people for protection, stealth... or may have some critters with them.
I was once excused from a gathering because I forgot to leave my crow buddies at home. Since I work shamanistically with spirits, it didn't even occur to me that my Wiccan hosts thought alternatively that I might be... funding an invasion of their hearth land, had more negative energy than I could shake a stick at, or c. wondered what I was hiding. For me, it was just habit to bring them along. What I didn't know was that to other people, a bunch of crow spirits looked... like big billowing clouds of black smoke. No one bothered to test it. Our alternate ways of interacting with the spirit world meant that we never saw eye-to-eye about what happened, even to this day.
So I mentioned that it's an energy structure. So what's it's shape?
Well, it's kind of ovoid in most people. Some people have shields,which can alter the size or the shape of their aura. Once you gain experience, you can see them. What's really interesting is that the aura fills up the space between their physical body, and the space we call 'personal space'. I suspect that the real reason people get unnerved when you go inside that inviable barrier is that you are standing in their aura. Seriously, you can mentally extend that aura pretty far from your body, and yet even ten feet away it's the same feeling of closed-in threat than you get when it's less than four feet away.
As for internal structure, you can make a few generalizations: they almost always flow like a fountain, from top to bottom. Think of the crown chakra as the crown of a water fountain and then that the energy flows up for a bit then gracefully flows back to earth in an arc. Under normal circumstances, it flows back under in a curve and winds up circulating through the feet and back up into the spine.
When you ground, you divert that return flow into the earth, and then pull the new energy back up through the balls (or arch) of your feet, or the root chakra...roughly around the knobby tip of your tail bone.
Your spine is a natural gateway for this energy up and down your spine. There are two concentric flows going up and down your spine at all times. This can be blocked, however, and that can cause discomfort, and sometimes other problems. Those blockages can come from emotional trauma, physical injuries, or even repressed memories forced to dwell in the body. These can either be drawn out by energy work or even a massage. The physical body frequently reacts to lingering issues in the energy body and can cause discomfort, and a blockage.
The standard model is that you have 7 chakras. Chakra Seven at the top of the head, Six at the center of the forehead, Number Five at the throat roughly around the Adam's Apple (or sometimes just below for women). Four is centered on the breast bone. Three is anywhere from in the center of your belly below th breast level, to from one to two inches above the navel, or sometimes around navel level. This can vary by gender, but it's not always accurate. Two is either centered or starts about two inches above the pubic bone. It is your center if you are a woman, or if you are 2 and dominant. Some people, usually men, are third-chakra dominant. Just because you might find the reverse doesn't mean that they are transsexual or something, it just means it's like the astral equivalent of being right handed instead of left handed, or having your internals in a mirror image. This does happen, but matters little. It may say that they are more ego focused than nurturing, or it might not. It's not a sure fire personality determiner.
The precise placement can vary, but these are again, the standards. Usually, if you are seeing the aura, you aren't seeing the chakras. It's just helpful to note that what ever you do see is the current of energy that flows through those chakras out in a wave. So it is a reflection of what happens inside you.
So, what about color?
Well, it depends. Some times, you see the colors that make sense to you. Sometimes you see the colors that make sense to the other person, and colors basically narrow down the possibilities some.
I personally see not only color but texture(grainy, or smooth; clear or cloudy), and I perceive temperature and added textural elements, such as a peculiar jangling tingly sensation which means chaotic vibrations. I get smaller, more regular tingles from a calmer energy.
This may or may not help you figure out what your system means, or if it's colored by what the other person feels about their colors. Usually, colors stand for what they might in magic, green or pink for love, gold or blue for spirituality, a darker yellow for mercurial tendencies or intellectual thought, etc.
Your mileage may vary. Frequently the other sights and sounds and smells or textures may tell you what you need to know to make some useful generalizations about the energies you are dealing with. Always take into account how you are feeling, and what kind of day you had, since when you are feeling tired, or weak, or hungry, you will tend to read things more hostile or aggressive than you normally would. Because the scale you receive has to do with your energetic well-being not always someone else's. SO if your energy sucks and you know it, your data may be skewed about what's going on around you on the spiritual level. Sometimes it pays to ignore some feedback (especially if you feel lousy) and study an energy field over time to see if it's really broken. See, it's flow that really determines how healthy an individual is. If there's a lot of stagnant energy, or a lot of pooling but not escaping energy, that's a true sign something is wrong. But too frequently, they assume that one color (or a set of colors) is always bad, and that if they feel uncomfortable there must be something wrong. Take a moment to separate your feelings about a person and how their energy feels. You might be surprised, as your personal feelings might well color your read.
Oh, and just because you can read someone's aura doesn't mean you know what they are thinking. You can see SOME of what they are thinking, but never the whys wherefores or even the how's all the time.
Because once you get into that territory, you've gone from aura reading to mind reading, and that is a different skill. They are related, however.
Reading an Aura, where to start.
First, it's hard to read someone's aura without their permission, tacit or otherwise. The most common way is to look deeply into someone's eyes, and then sort of defocus a bit. Then step back one, then two if you aren't far back enough. This works best in a not-so-well lit room, or with dark walls. Oddly, witches who wear nothing but black are doing you a favor, and making it easier for you to read their auras! Conversely, white can also make it easier, depending on how your perception works.
So, why can't you? Well, reading someone's aura can work one of two ways. The first, and most common is sort of like doing a surface scan on someone's mind.
Either that, or you can work at it from an empathic channel, where you are just very sensitive to the other person's energetic output. This is kind of like being able to see inferred or something like that. You can not only read a person's aura but that of a building, a stone, or practically anything. This is the rarer form, and also much harder to interpret, since you don't get help and you see a cascade of energies and have to basically filter that person out from the rest of the room, your conventional sight, and yourself. The projective reading of auras is actually in some ways much simpler. It's also less of a headache, quite literally. You are also much likely to see a persons energies as they see them, which means a potentially new map for every person you meet. Fortunately, most energy workers use the same system, so you can cheat most of the time. But always be on the look out for things that aren't quite within your experience and try to broaden your scope and knowledge of energy patterns.