Your average layperson would probably not realize that there is more than one type of dragon. A dragon is a dragon, right? They fly around and breath fire on knights, sometimes hoard gold and that's it. Right?
Nope. In D&D there are a crap-ton of Dragon types. All separated by color, which is a little racist but there you go. Most of the "evil" dragons are chromatic colors. The big five bad guys are: Black, Blue, Green, Red, and White. Most of the "good" dragons are metallic colors. The big five good guys are: Brass, Bronze, Copper, Gold, and Silver.
Each type/color dragon breathes a different type of breath weapon. Red breathes good ol' Fire. Black vomits out an Acid spray, Blue "breathes" lightning bolts (don't ask), Green breathes out Chlorine gas, and White breathes out Frost. The good dragons breathe out ridiculous stuff like sleep gas and slow gas and something called "repulsion" gas. Kinda dumb if you ask me. Good dragons aren't that interesting.
So which dragon is my favorite? Some would guess its the dreaded Blue dragon since Quinn spent years seeking out a Blue dragon as part of a quest to create the ultimate undead-killing sword? Sadly, no, he never did find that blasted Blue dragon, he was too busy saving towns from ghoul packs and vampires.
No, my favorite Dragon is the Black Dragon. They're really cunning but not conversationalists, making them a verified "monster" and not something you'll end up playing chess with or answer a riddle or something to survive an encounter. No, Black Dragons hide and hunt in swamps and they spray acid everywhere and melt stuff. That means if you've got Black Dragon infestation outside your hamlet you know it pretty quick, because there'll be melted cows and stuff as evidence. But Black Dragons like to hide in swampy undergrowth so its not like they're easy to just see before you get acidified. Kinda like a Medusa, it easy to figure out what kind of monster you're facing, but still not super-easy to find and kill. Good plot trigger for monster-hunting adventurers. The kind of problem a town Burgomeister would hang an "Adventurer's Reward" poster for the hunting down of the "Acid Monster." Plus just hunting a Black Dragon means you're going to be fighting a very dangerous monster in a swampy area, giving a great opportunity for all sorts of slippery terrain or waist-deep swamp water or other fun combat problems.
So here's to the Black Dragons!