You can change your color. Your aura can be determined by holding your hands open fingered away from your face and peering between the spaces of your fingers. The next time you look at it though it might be a different color. They fluctuate. It'll take a few times but then you'll get it. Some people locate it also by looking at a mirror at about an inch- inch and a half away from their skin but I found the finger way works the best.
The colors all mean different things. You'd have to look online at a page devoted to it.
Aura is the emotional energy one gives off. Example if some one is angry they give off red or depressed is blue. As for seeing it on other people there are several tout oriels online and it can be learned by most in under a week.
The previous poster explaned the colors really badly, each color has like a 1000 shades each with a meaning and bloo typically isn't depressed but com cool collected, in some shades a sign of enlightenment in some healing and red also has various meanings depending on the shade but typically does mean engry