This a minor point of minutia, really. And be warned, as the headline suggests, it's alignment-related, so it's going to be stupid-ish.

Question: Can anyone think of a published (I'll even take Dragon/Dungeon magazine) instance of a Chromatic or Metallic dragon that definitively didn't match the normal alignment for their breed?

I have an elder wyrm red dragon in my campaign, but players have more or less figured out he's probably Lawful Evil rather than Chaotic Evil. He's a fairly long standing part of my campaign world, and most players over the years (that gave him any thought at all, depending on where in the world they are) have never had an issue. But players are finally actually in an area where he's relevant, and I've got a couple of "we've read the Monster Manual for fun a few too many times" types that are pointing out his behavior is way too indicative of a Lawful alignment.

This is, I realize, the epitome of "who gives a shit" nerd squabbles. I'm just curious if anyone can remember an example from the "good old days".

Closest I can think of is Wormy the green dragon who did not seem to be Lawful Evil.
https://en.wikipedia.org/wiki/Wormy_(comic_strip)

The Dragonlance novel The Gully Dwarves (1996) focuses on a reformed green dragon, rejected by Takhisis, Verden Leafglow. Verden Leafglow took on a "verdigris" or "amber" hue, and was eventually "reborn" as a bronze dragon through the divine intervention of Reorx.

Pretty much all the dragons in BX D&D as nothing was actually locked down in alignment.

Moreso with the Council of Wyrms setting.

Mystarra had an article on various dragons and theres a well known blue dragon I believe with a love of music and has become a sort of patron of musicians and bards.

Probably the very first occurrence is the, I believe, copper dragon in Quag Keep. Been a long time so might be wrong on type.

I too would have to refer back to AD&D (1e and 2e) as well as other TSR era D&D.

The one that really comes to mind is from Dungeon Magazine were an albino red dragon moves into a region and the DM is encouraged to let the players believe that they will be facing a white dragon.

But there are other instances as well of good Dragons turning out to be evil and evil Dragons turning out to be good. If I remember correctly there is an example of one or the other (forget which) occurring in the 2e FR supplement "The Draconomicon".