My favorite dragon encounter was a dragon that I still don't know the species of. The damn thing was puce. My DM didn't want us to have any meta knowledge.

It was fun though because of how we got to, and dealt with, said dragon. Dragon was in a mountain lair that, when scryed upon it was revealed, was full of traps and minions.

My wizard figured out that she had just enough 8th and 9th level spell slots to cast Xorn Movement, and Improved Invisibility on the entire party (no invisibility on herself though), and still have 2 casts of Unfailing Missiles (9th level spell she created). We successfully snuck into the dragons lair, and took positions. Our monk was ready to grapple its tail, our rogue was ready to backstab, and was flying because he had a magic item, our cleric was prepping Harm,and our fighter was annoyed that I put her behind myself.

I tapped said sleeping dragon on the nose, and said in Draconic, "Wakey wakey." The dragon opened its mouth to use whatever breath weapon it had, and I said, "That's not a good idea, that will just make me and my friends angry."

The dragon then realized I was speaking draconic and parlayed with us. We explained that we didn't even want to be there, but the gods had tasked us with the eviction of the few dragons that weren't supposed to be on this particular prime material plane in the first place. We also explained that we had brought with us 20 empty bags of holding, and would prefer to relocate them off the plane to a plane of their choice. Thankfully that dragon took the deal. The other three ended up with their souls in rather large black diamonds, that the God of Knowledge had provided us.