i never saw ani dissappear either. and the saber that was givin to luke was said to be ani's before he was vadar. it was blue right, just like obi-wans when he was training with qui-jon and qui's was green like lukes when he was a jedi. i cant remember the color of obi-wans when he fought vadar but maybe it has something to do with learning the force and knowing the force.
Also remember that we (or some of us) had to wait 6 years just to see another color than blue and red.
I still think we will se other colore, it would be strange not to see several colors.
BTW Obi's saber was blue in ANH. That blows the blue= padawan Green = Jedi Master theory.
Luke only got a green saber because it didnt look right in the desert scenes.
If Luke became a master on his own. I would think that Obi would have also.
Maybe he just liked his saber so much that he never changed. But I still think the colors dont have anything to do with rank or belief in the force.
And I'd think its highly unlikely that Luke borrowed some of Qui Gons saber. Making a saber is a very personal thing for the Jedi to do (another reason for mutiple colors) and he would have to have done it from scratch in order to become a Jedi himself.