you have to read the Unfinished Tales chapter "The Istari." There were
actually five Istari sent to Middle-earth, chosen by the Valar.
Aule chose Saruman (Curumo), who was their leader, and Orome chose Alatar (one
of the blue wizards). Manwe himself chose Gandalf (Olorin), who didn't
want to go because he thought himself to weak to go up against Sauron.
Varda intervened. With two more to chose, Yavanna insisted that Radagast
go with Saruman, probably because of his love of nature, and Alatar chose his
friend, Pallando, to go with him.
There's a link below to The Encyclopedia of Arda. Scroll down the left
side, go to the 'I' section and click on 'Istari.' There's lots of
subsequent links that will keep you busy for a while. But, the best thing
would be to get a copy of UT and read that chapter!
Have fun.
p.s. It still doesn't solve the question of what happened to the two blue
wizards, so your theory is as good as any.
;)
