Dneecey, it's my opinion that yellow aura's just mean you were excited about things at the time, maybe talking fast, or just moving a lot. When people are speaking, they tend to emit yellow. When you are deep in concentration, you'll likely emit it too. I think aura's change, but your 'core' colors stay the same, unless something drastic happens. One of the reason I dislike this subject is that there are so many descriptions of what the colors mean. I don't think they can be defined in a book, I think, like Maetel said, they can only be defined by the person seeing them. For example, I've read how 'red' auras are 'exciting and powerful and dynamic' but if I see someone with red, there is a really bad feeling that comes from it, and I will avoid that person like no one's business. Also, everyone talks about purple being spiritual, but purple just makes me uncomfortable. I've read that white is both truthful, innocent, and also, sick and about to die - but I think white is spirituality - unfortunately, if seeing auras is really possible, I don't believe there is a guidebook that's helpful. It's 100% intuition.
Being someone who can see aura's, I still have to tell you I'm skeptical as much as interested. When people see 3 headed monsters in their living room, they're delusional, when someone sees colors around a person, they're psychic. I both listen to my gut instincts about people when I see their auras, but I would do that anyway.... I have gut feelings about what the colors mean, but I also can't say that I'm not making it up. LOL, unhelpful I am.