Here’s an essay from my Random Dungeons book, which you should buy! Lots of stuff there, by me and other authors, which doesn’t appear on anyone’s website.
metallic dragons are from the planes
Metallic dragons never seemed to me to occupy the D&D world as chromatic dragons did. While fighting evil dragons is a core D&D experience, interacting with friendly gold and silver dragons sometimes seems hokey.
For one thing, a D&D world doesn’t have room for a lot of super-powerful good creatures. You might as well have a race of Elminsters running around, solving problems before the PCs can get to them. Even if they’re more Switzerland than global policemen, they still add areas of stability and safety that don’t have a place in every campaign world.
Also, the metallic dragons, with their ability to disguise as humans, seem to be on a different level of reality than the straight-ahead evil lizard cousins. They remind me of the Golden Hart from the Blue Rose d20 system: more like magical guides from fairy tales or hero’s journeys than inhabitants of the natural world.
I think that the metallic dragons have a place in D&D: and that place is the planes.
Gold dragons belong in the realms of the gods: the Astral Sea or the good-aligned outer planes. These dragons, like their home planes, are almost too beautiful to view directly: the sight of half-a-dozen winging across the glowing astral clouds is one that will stay with viewers until the end of their days. Gods and their exarchs sometimes ride gold dragon allies into battle. A gold dragon in the natural world is, perhaps, on an errand, doing a favor for a god.
Silver dragons are native to the moonlit glades of the Feywild. They’re among the most powerful and unpredictable natives of that powerful and unpredictable place. I like them as the most powerful dragons of their plane: it seems like a more interesting niche than “the second-most powerful good dragon”.
The other three traditional metallic dragons are brass, bronze, and copper, which is a bizarre collection of metals. We have way too many indistinguishable copper alloys here. There are five metallic dragons to match the five evil dragons, but, to me, these three don’t seem to have distinct conceptual places. I’d get rid of brass and bronze, and just keep copper dragons.
As gold dragons reflect the radiant light of the sun and silver dragons the moon, copper dragons suggest to me firelight. I actually think that copper dragons might belong in the natural world: they’re less powerful than many of the evil dragons, they’re described as gregarious, and in some editions they have stone-related powers. They might need to hide from the evil dragons to survive, and they split their time between hiding among humans in cities and skulking in vast torch-lit caverns under the mountains.
Maybe every dungeon, or many of them, contains the hidden lair of a copper dragon. You’re not likely to find it without really thorough exploration and possibly a stroke of luck.