Since this is apparently a thread for flogging dead horses after they've long since died, I'll give a few more kicks to the carcass sitting next to me.
Dragon symmetry is one of the least excusable D&Disms in the game. By establishing an unwritten rule that the most defining characteristic of a dragon is his color, lousy dragon design is assured.
First, it creates the need for a LOT of different types of dragons. And once you've done that, you need to give all those dragons characteristics that are actually different. So you assign them things like environments or breath weapon types or whatever based on lists: "Well, we've used up most of the logical environments, and we still have a blue dragon. Lets, um, put him in the desert? Royal blue, lightning, and deserts go together, right?"
Second, it ensures that D&D dragon art is uninspired. Because dragons are defined by color, they end up being nearly monochromatic. You basically never see scale patterns or anything. And this is in spite of the fact that lizards and snakes are some of the most colorful animals in the world. A wealth of inspiration is available for the taking, but it never gets used because someone decided that dragons were one color, and one color ONLY. I want dragons with diamond patterning, dragons with leathery, tiger striped skin, dragons with whatever! Something other than monochromatic design.
The only good thing that has come from the color wheel dragon design philosophy is interesting dragon body shapes. Deprived of the ability to vary dragons in appearance in any natural way, dragons had to be varied in appearance by the shape of their bodies, the type of horns or tusks they had, and the shape and design of their wings. I approve of this, even if, overall, the process by which we got here was kind of lame. I do tend to think, though, that this occasionally goes too far, and perhaps it wouldn't have to if dragons were designed using more than one crayon. I mean, they wanted to make the green dragon look scary and toxic, so they slapped a billion horns on its head sticking out at odd angles? I get the logic, but wouldn't it have been easier and cooler to give it orange poisonous-jungle-frog markings on its back? But nooo, we can't mix orange and green. Its against the dragon code.
Instead of starting with a name and deriving a concept, better design might start from a concept, then derive the name. For example, we could create a Desert Dragon. What does it look like? I don't know, what fits in a desert? Tans with a pattern? What breath weapon fits a desert themed dragon? Fire for heat? What about burning ash? What about skipping the breath weapon in favor of a poisonous bite?
There are a million possibilities that we'll never see because we're so busy filling out a grade school color wheel.
*hauls dead horse to the dumpster out back*
Editted to add:
Look! A crocodile themed dragon! What will they think up next? And by "they" I mean, "not WOTC."
http://www.coolminiornot.com/190