Admittedly, that's something I've attempted to step away from but have failed in doing so as much as I'd like.
Even when running other game systems, it's become a shorthand way of trying to give players (who have experience with D&D and color-coded enemies in video games) some hint about what to expect from a dragon encounter.
My intent is usually to hint at what sort of attacks they'll face, but I suppose I've also participated in pushing negative ideas about outward appearance.
I do have some ideas for doing it differently, but I'm not sure that putting energy into completely reworking my usual audience's understanding of a core aspect of their fantasy experience would be fruitful. Some of them had a rough time with the idea that dwarves I had in a setting weren't Scottish Vikings.
Terrible excuse I guess, but

I win the battles I can and try to support my real world beliefs while also realizing that I'm playing a game that involves other people, some of whom just want to roll dice and not think too hard about whether black dragons living in a swamp is some manner of racist social commentary.