Concerning how a person is chosen to be a Rider:
It is commonly thought that a person's parentage affects their chances of becoming a Rider. However, many, or even most, of the Riders had might not have Riders for parents. Probably the best reason is that it still depends upon a dragon in its egg to choose any given person as its Rider. Hence there exists no absolute chance of the above being true. This idea may have taken root from the fact that both Morzan's sons became Riders.
Paolini confirmed in a March 2006 interview that when a dragon and Rider become linked, the Rider's magic immediately takes on the color of the dragon's scales. However, this does not mean that if you are a magic user born with green energy, you cannot be paired with an amethyst-colored dragon, for example. On being linked, your magic will automatically change from green to purple - although you can change colors at your will. Paolini states that although Eragon's magic is blue, he could produce red fire if he wanted to. So far, however, Riders' have chosen to use the automatic color - their dragon's color. Oromis uses gold magic, Murtagh's energy is ruby-red, and Eragon's is bright blue. Shruikan is black, although the dragon that actually chose Galbatorix might have been another color; the union between Galbatorix and Shruikan isn't a true dragon-Rider union, so Galbatorix's automatic color may still be that of his original dragon's, though he may have chosen to change it after so many decades.
There is popular speculation about Arya of the Elves being the next Dragon Rider, as the last unhatched egg contains an emerald male, and Arya's magic is green. However, the revelation made by Paolini in the March 2006 interview (over live chat) means that Arya may not necessarily become the next Rider just because her magic is green - another may be chosen, and their energy would them automatically give green magic. Supporters of the Arya theory also argue that she has green eyes, although the significance of this is debatable. Something that would aid the speculation that Arya could be the next rider would come from the dream that Eragon has which shows two people going on a boat leaving Alagaesia while two dragons are flying above; this ties in with the prediction made by Angela that says that Eragon will leave Alagaesia never to return.
Also Eldest: Limited Edition is set to release on September 26, 2006!