Was the White Guardian involved in the Key to TIme at all?

Question

In the "Key to Time" epic, covering the whole of season sixteen of Doctor Who, the Doctor is sent on a mission to retrieve the six pieces of the Key, ostensibly by the White Guardian. However, he is not the only person looking for the pieces.

The third story, "The Stones of Blood," begins with a warning voice: "Beware of the Black Guardian," which is the first mention of the Guardians since Romana's arrival in "The Ribos Operation." The Doctor then visits contemporary Earth, where the third segment has been held by the alien criminal Cessair** of Diplos, having brought it there thousands of years earlier. And Cessair knows both how to use the segment's shape-changing powers to alter her appearance, and that the Doctor is there looking for the segment. The natural conclusion is that she is an agent of the Black Guardian, who is seeking the key.

In the last story, "The Armageddon Factor," the main villain, the Shadow, makes no attempt to hide the fact that he is a servant of the Black Guardian, and that he has been waiting for the Doctor to arrive with the first five segments of the Key. ("I am the Shadow. Your adversary, shall we say. It is not important. You come in quest of a key.") At the end, with Shadow, in death, calls out to his master for help, but the Black Guardian disguises himself as the White and goes to claim the complete Key to Time from the Doctor and Romana.

My inference, from the first time I saw the stories, was that the whole storyline was entirely the work of the Black Guardian, that the figure who gave the Doctor his assignment in the first story was not the White Guardian, but again the Black in disguise. So the Doctor, Cessair, and the Shadow were all working for the same power, knowingly of not. This explains, for example, the curious fact that Cessair of Diplos had captured one of the segments and brought it to the Doctor's favorite planet; it was there waiting for him to swing by and claim it.

However, in a number of online discussions of the season-long plot, I have seen the suggestion that the White Guardian really did put the Doctor on the job, and that he completed his adjustments to correct the coming chaos in spacetime while the Key was complete, before it was nearly stolen by the Black Guardian. My ultimate question is whether there is there any evidence for this idea in the stories? Or is this just a product of people misunderstanding a somewhat subtle plot?

** Only today, as I was researching this question, did I learn that "Cessair," like several the villainess's other identities, is the name of a Celtic heroine/goddess.

Answer 1

I am not fully aware of what is considered accepted canon sources in the Who'verse, but everything that I can find corroborates that it is the White Guardian that sets the doctor the task originally.

From a transcript of the show (Admittedly the Guardian could be lying):

GUARDIAN: I am the White Guardian. In order to maintain the universal balance, there is also a Black Guardian, and he also requires the Key to Time, but for a different purpose. An evil purpose. He must not get it. Doctor, at all costs, you must prevent that.

From The Doctor Who guide:

The Doctor and K-9 Mark 2 are sent on a mission by the immensely powerful White Guardian. The six segments of the Key to Time, currently disguised and scattered throughout the cosmos, need to be brought together. Once assembled, the Key will allow the Guardian to restore balance and good to a universe that is descending into evil and chaos. It will also thwart the plans of the fearsome Black Guardian!

From TvTropes:

A godlike guy in a casual white suit, the White Guardian, interrupts the Doctor's puttering around in the TARDIS to give him a quest: find all six segments of the Key To Time. Why and how and what the thing does isn't explained just yet, but the Black Guardian apparently wants it too.

From The Den of Geek:

If you really want to break out the big guns, you can argue that Season 16, during Tom Baker's tenure, was the longest story in the show's history, running for twenty-six episodes.

The Doctor is enlisted by the White Guardian to find the six separate segments of the object through time and space, and assigned a Time Lady companion, Romana, to help.

Probably one of the stronger corroborations is from a book titled The Doctor Who Programme Guide by Jean Marc Lofficier (I was unable to find the actual episode excerpt in google books, this is from a synopsis on this site):

SEASON SIXTEEN

  The Ribos Operation                    9/2/78    9/23/78    4

Sent to seek out the Key To Time by the White Guardian, the Doctor and his fellow Time Lord Romana, find themselves sucked into a botched mineral scam on the planet Ribos.

Answer 2

It's not a full confirmation, but the Black Guardian himself actually gives us the best indication that the White Guardian was able to fix things while the Key was assembled.

The Doctor is able to confirm that he is really talking to the Black Guardian at the end by asking about Astra, and pointing out that, as part of the key, if it were to be kept assembled, she would be trapped within. The Guardian admits this to be the case, but dismisses it, as 'the fate of the universe' is at stake. As the Doctor then points out to Romana, the White Guardian would not have been so cavalier about Astra's fate, and would have complete his work and dispersed the key.

But right before that, while acting as if he believes he is talking to the White Guardian, the Doctor has the following conversation with him.

Doctor: "What happens now, sir? You said, if I remember our first conversation, that once it was assembled it would stop the entire universe and enable you to restore the natural balances of good and evil through out the whole of the universe."

Guardian: "That is correct Doctor. So will you release the key to me that I may do this?"

[The Doctor starts to command the Key to time, but then stops and asks another question]

Doctor: "It's just that, well, the key is already assembled, sir, couldn't you restore the balances now?"

Guardian: "Yes, Doctor. But I must have the key... for safekeeping."

As I read it, that 'Yes, Doctor' is confirmation that the White Guardian's task just requires the key assembled; the Black Guardian, however, has further plans for it. The Black Guardian could, perhaps, have interfered, but he was working a long-con on the Doctor and trying to get permanent possession on the key, while the White Guardian just needed it activated with the Black Guardian distracted by his attempt to get the key from the Doctor allowing him to complete his tasks unopposed.

Follow-up Checking back to the Doctor's original encounter with the White Guardian, he, too, indicates that time need be stopped 'For a brief moment, only.' I don't know why the Black Guardian would say that, were he to be impersonating the White Guardian at that point, as it undermines his need for the key to be given to him, but it's possible he is trying to use as much truth as possible, with the single lie of his identity set to reverse everything. This is supported by the fact that he indicates a moment later that the pieces need to be returned to him, which is untrue.

All said, I don't know if we ever saw the White Guardian; it could well have been the Black Guardian the entire time. If so, the White Guardian seems to have been betting on the Doctor's perception to allow the White Guardian to complete his task while the Black Guardian engaged in a fruitless attempt to gain the key for himself.

Very genre-savvy of the White Guardian.