The colours of the Istari
The Istari were sent to Middle Earth in a rather odd arrangement in that Saruman, Alator, and Pallando all arrived first and immediately headed to the East. Of these three, only Saruman returned. Next arrived Radagast the Brown and then, the last, was Gandalf.
Their colors are interesting in that Saruman, Chief of the Order, wore White. The two that sailed with him were Alator and Pallando and they BOTH wore sea-blue. Radagast wore brown, and finally, Gandalf wore grey.
There may be no significance whatsoever to their colors, but I believe, in researching a magic system, it is worth looking at for a moment.
As in Druidry, White is the color for the most learned or Chief of the Istari. Saruman wore this color first, but when he adopted "many colors" and turned to darkness, Gandalf, after surviving the battle with the Balrog, then took the White robes. In doing so, Gandalf became Chief of the Istari, (though there were only two left!!) White is a color of power in that it is pure, it reflects, and it is all and also nothing. It is the Alpha and Omega, the womb and tomb, the birth and resurrection.
The next two Istari BOTH wore blue robes. I find it fascinating that BOTH wore the same color. In Druidry, blue is the color of the Bard, the keeper of the histories, the poet, and the singer. Did Tolkien know this of the Druids and therefore make the color of these Istari similar? Actually, I doubt it very much. Yet, I also doubt it's coincidence that these particular colors were chosen in general. So, were Alator and Pallando akin to Druidic Bards?
Next to arrive was Radagast. I think it was no accident that the Valar had him wear Brown, like that of what we call monks, in that Radagast was very much like the Hermit monk so well known from Medieval literature tales. Brown well suited Radagast and his "earthy" tendencies. He was a caretaker, a lover of animals, and a speaker with beasts. He could almost be called a Cernunnos or Green Man, except that he was more gentle than those two Wild spirits!
Gandalf was the last to arrive, Olorin he was called in Valinor as a Maiar, and it is said that he was the "wisest" of the Maiar. I believe that the Valar were able to foresee that Gandalf would directly affect the outcome of the battle with Sauron, and though they might not have foreseen Saruman's betrayal, they may somehow have known that Saruman would NOT be the one to lead the Free People's to peace. In doing that, they sent Gandalf wearing grey, a color of black and white mixed, to show the balance within him. He did later take the White Robes as Chief of the Istari to show his dominance over Saruman.
It seems that each Istari had his weakness as well. Saruman was fascinated with the Rings of Power and devoted much of his life in Middle Earth with their research. It was his fascination that led, ultimately, to his undoing, and nearly the undoing of all of Middle Earth, for Saruman fell under the power of the One Ring, even though he had NEVER held or BEheld it! JUST by studying it, lusting for that power, imagining what that power could be like on HIS hand, Saruman was corrupted. He yearned to become like Sauron and rule all of Middle Earth - all of this and he never actually saw or touched the One Ring!!
Radagast was fascinated with the beasts and birds of Middle Earth. Though this fascination did not lead him down a dark road as Saruman took, it did lead him away from his purpose as an Istari, and thus, left the burden solely to Gandalf.
Gandalf was fascinated with hobbits and hobbit lore. Quite odd, for an Istari, wouldn't you say? What led Gandalf to pick Bilbo as the "thief" for Thorin's Dwarves? Did he somehow know that Bilbo would find the One Ring? Perhaps on some subconscious level, for he clearly states that he was not even sure that Bilbo's ring was THE ring until well after their Dwarven adventure was finished. Rather, I would believe that Gandalf was guided by Fate, or the Valar, to venture into the Shire and choose a hobbit to go with Thorin.
Did the Valar then know that the One Ring was hidden with Gollum beneath the Mountains? I doubt that, too, yet they probably had some sense that the Ring was indeed found when it slipped from Isildur's hand and that it would, in time, resurface. They probably knew that a halfling had something to do with the Ring after Isildur, but other than that, I do not think that they knew anything for certain. However, it was Gandalf's "odd" fascination with the Halflings that, in the end, saved all of Middle Earth.
Were the Istari akin to Druids? Yes, they were, especially in their roles of caretakers and prime movers, judges and counsellors.