I was reading Dragons Revisited, and it mentioned the possibility of metallic dragons going bad or chromatc dragons becoming good. I was curious, but I couldn't find any further discussion of the topic within the book, and the only relevant thing I could find when I googled the subject was less about how and more about what colors metallics would become/metals chromatics would become upon an alignment shift. So, as my question: Does anyone know about any discussions/in-book examples about dragons changing alignment(Being Redeemed or Tarnished), and if not, could you put forth possibilities for the circumstances behind such an event?

I suppose it could be any reason really, as alien as Dragons are portrayed they usually have "human" motivations, say a Gold Dragon foresees a great disaster that will lay waste to the land emanating from a small village, it can't perceive specifically where and who starts it but for the sake of the whole it lays waste the village. Of course it can't openly murder such lesser creatures, but it can "influence" another humanoid to do it. Soon the Dragon is seeing the merits in stopping disaster from happening and before long is overkilling for the self perceived thought of stability.

Heck I've had a Senile Red Dragon as a good NPC, one of my players wanted to have sorcerer with dragonic blood in his family history, seeing as how old Dragons can live she was still around, albeit extremely old, so the party would alway run into this old lady in small towns. The best was when I randomly dropped a Hill Giant and the Dragon swooped down and snatched the giant away, it freaked the party out and left them wondering if they had to fight her.

Okay, so...I've got 'varied' and 'Gold dragon thinks tarnished actions are for greater good'...
Anything else?

Maybe Pathfinder dragons aren't racist and simply have motivations not driven by the color of their scales?

The Bestiaries and Dragons Revisited suggest otherwise. I'm not opposed to tinkering with a race to suit my own purposes (For example, making a Pathfinder game where color really doesn't matter for dragons), but my curiosity was geared towards Pathfinder dragons as presented in the books.

A brain tumor pushing on various parts of the brain or a head injury can cause changes in personality, mood, and behaviors.

Which could result in an alignment shift for good or bad. And an interesting plot twist. The PCs battle a gold dragon doing terrible things. Perhaps one with a history of good deeds. Can either kill it. Or might somehow cure it. For even more benefit. (Or it may then 'retire'.) A normally evil dragon may do some good. Take an arrow to the head near the end of a battle with a stout enemy. A Cure / Heal spell to the area suddenly results in a new stout enemy to fight. ....

Heheheh, brain damage for morality. Nice.

Couldn't help but be reminded of and mention the humorous (and somewhat beneficial to hear, but more humorous) song Albi the Racist Dragon by Flight of the Conchords. Google / You Tube for a good listen if you have time.

Which is about as close to relevant to this discussion as something so purely humorous can be. And provides such valuable (though perhaps non-canon) insights into Dragon alignment as the 'fact' that "As we all know" Dragon tears turn into jelly beans.

And provides yet another plausible cause of an alignment shift for a Dragon. An unexpected and surprisingly productive discussion about his own (and others) racism with the badly burned Albanian boy he thought he killed yesterday.

Helm of Opposite Aligment is a possibility. Otherwise, mental sickness and/or intense emotion(grief, anger) could probably change someone's personality so I'm guessing it could happens to dragons.

A buddy of mine did some research on the topic and looked into Terendelev, the silver dragon native to Kenabres Mendev (and starting area for the Paizo written adventure path Wrath of the Righteous).

In some of the lore of Kenabres before Pathfinder was officially Pathfinder (Paizo used the 3.5 rules at first), Paizo went into the lore of Kenabres and described Terendelev in detail, and also how she was starting to tarnish. The jist of that situation is that a tarnished metallic dragon is a dragon that has lost all hope in doing good, and have a mentality of "What's the point of doing good when all things come to an end anyway?" As a result, their scales become less vibrant, less metallic if you will, and become tarnished. Thus the term.

Redeeming a chromatic dragon is then the exact opposite of tarnishing a metallic dragon. Redeeming a chromatic dragon is when their mentality shifts from, "I will sow destruction and personal gain," to that of a classic metallic dragon, aka being a beacon of good and preservation.

Let it be known though that tarnishing or redeeming a dragon is by no means easy, and the difficulty of tarnishing or redeeming a dragon changes depending on the color, and I'd strongly recommend doing a bit more research on the matter. There's likely a wiki on tarnishing or redeeming dragons, and at the bottom the sources are listed. Look for the titles of those source books then head to The Trove and find the books in there to read. I'd include a link to The Trove at the end, but myth-weavers won't let me as per their guidelines (must make 5 posts before being able to add links and stuff).

For an example as to how the difficulty changes from dragon color, in all of Pathfinder lore there is only one tarnished Gold Dragon (Trilochan if I had to guess, the gold dragon servant of Rovagug). Likewise, there is only one ever redeemed red dragon (whose name I don't know).

I hope I was helpful.