|
I think that it is because a white oliphaunt would be distinguishing, and also becuase white is seen as the color of good. Also, white is one of the few colors that makes sense. What could Frodo say? "I wish we had a thousand oliphaunts with Gandalf on a blue one at their head"? That doesn't make sense. The distinguishing colors that you are left with are probably black, brown, and white. And for JRRT's purposes, white worked best. Though I suppose he could have been tying it in because Gandalf was the White, even though Frodo didn't know that.
|