I am working on my own homebrewed Fantasy Mexico inspired D&D Campaign set in a facsimile of the historical Spanish Conquest but dragged out longer like both sides are pretty evenly matched with the backup of Gods and Magic.

I decided to make my own group of 5 original Dragons for the setting based on some of the Aztec Gods. The Rainbow Dragon is based on The Feathered Serpent himself; Quetzalcoatl.

Quetzalcoatl is probably the best known Aztec God, if you know anything about Aztec Mythology, you probably know Quetzalcoatl. The image of the Feathered Serpent deity is actually very old long predating the Aztecs themselves who were late comers of the pre-colonial Native Mesoamerican civilization, and because of the widespread appeal and universality of the Feathered Serpent God, it made them a connecting point for many different Central American civilizations to promote diplomacy and trade.

Each civilization had their own interpretation of the Feathered Serpent, but it usually has some recurring themes: being a Serpent with Feathers meant they are connected to the Earth and the Sky so they could be connected to mortals and the heavens, and also usually embodies resurrection with Quetzalcoatl specifically having multiple birth stories that don't overlap one another and can be taken as different incarnation of the same God.

To the Aztecs, Quetzalcoatl is one of the 4 most Primordial deities called the Tezcatlipoca (Although confusingly only 1 of them is actually named Tezcatlipoca, and he is the problem child of the bunch). They were responsible for the creation of the world, and Quetzalcoatl specifically was responsible for creating Humanity by sacrificing some of his own blood. While most Aztec gods are known for their bloody sacrifices, Quetzalcoatl specifically did not approve of any human sacrifice and was kinda disgusted by the idea. Instead he preferred smaller offerings of Food, Cocoa beans, and Sea Shells.

He is the Patron of Art and Artists, Musicians, Craftsman, Artisans, Merchants, and Priests, he Promotes Knowledge, Justice, and Mercy, and he seen as the builder and connector of civilizations.
Basically he is a very nice sky noodle who loves humans and would probably display our art on his fridge and show it off to other gods.

These Dragons do not come into being the same way as other Dragons in D&D. In Aztec mythology the gods would often reward their followers by resurrecting them in new forms, like how Warriors who have fallen in battle were honored by being reborn as Huitzilopochtli's Hummingbirds. Humans were created from Quetzalcoatl's blood, so maybe within this setting the stand-in of Quetzalcoatl can pick human follower they believe have shown qualities that exemplify their will and resurrect them post mortem as a Rainbow Dragon by activating the already present aspects of the Feathered Serpent that lie dormant in their blood.

These dragons retain their memories and personalities from their human lives. Rainbow Dragons are typically the most friendly and approachable dragons, and enjoy being involved in social gatherings and events.

They have a Radiance Breath Weapon and the ability to control the Wind.