Huh. Turns out I have quite a few dragons that are the only ones with their colors still active on the site. The rarest is this guy, a yellow/clay/chartreuse bred by my kiddo (who is an excellent source of random color combinations).
There have only been two other dragons with this combo, and they were both exalted without offspring. He's the last one standing.
Others in my lair who are now unique on the site:
Gangrena, cinnamon/moss/chartreuse, one of 4, others exalted
Blaze, grey/marigold/camo, one of 4, others exalted
Starlight, bubblegum/maroon/algae, one of 4, others exalted
Sparkler, sunshine/teal/ginger, one of 5, others exalted
Peacock, leaf/carrot/honeydew, one of 7, others exalted
Boreas, smoke/antique/seafoam, one of 7, others exalted
Nasturtium, carrot/blood/umber, one of 8, others exalted
Pyxidis, fuchsia/dust/umber, one of 8, others exalted
Rasberry, carmine/honeydew/carrot, one of 9, others exalted