Star Wars questions ?

I think the reason why obi wan and qui gun jim disapear after they die is because they are the masters and they leaders however I'm not sure. I'm not sure why the sith used the red lightsabers maybe because the color red is made for evil? I just love the movies. I'm a huge star wars fan. Those are my guessed though. I don't remeber any chick with white hair or a yellow alien.