"Gandalf on a white oliphaunt"

[doug*platypus]

the publishers probably had an army of monkeys chained to desks

Agreed. That's what I would have done!

Yes, white is definitely the colour of good in the world of Middle-Earth. Good is always white, silver or golden and shines. Evil is always black and dark. Letters (can't remember which) makes an interesting point... that evil isn't evil because it's black. It's the other way around: evil appears to be repulsive and dark because it is evil. Likewise, good things or people such as Galadriel, Glorfindel or Frodo seem to shine because they are good.

Perhaps Frodo saw the inner light of Gandalf that was always hidden by his old, grizzled countenance and his grubby grey cloak. He did, after all, foresee the appearance of Gandalf the White in the Mirror of Galadriel.