The bad thing is not KNOWING one's aura. What's bad is restricting your RP to "OMG u r darkie, I not talk 2 u, u must die in fire!!!111```". I have often been in such a tough place playing aberrant characters, who yes, are evil but also have principles (even though often distorted) that they follow, and quite often they will do what a lightie would consider as "good".
Mechanics wise, and as long as I am aware, there are indeed a means to fool people about your aura. Still, this is not the answer. The solution imho, is to keep in mind this piece of information about one's aura if you have the option to, but like in real life yes, be weary about his "general attitude" if that's what you could call one's aura, but do not isolate him because of that alone. It's like IRL someone has been to prison (probably for a crime he has committed in the past although you don't know what the crime is) and keep him away or even hunt him just for that. Now, that's not exactly the model of "lightie" behavior, is it?
