Chromatic Dragons are one of the many specific breeds of dragon native to Dungeons & Dragons and Pathfinder. They are one of the two most iconic family groupings of D&D dragons, alongside the Metallic Dragons. Lesser D&D dragon families have include the Catastrophic Dragons, Ferrous Dragons, Gem Dragons, Oriental Dragons (or "Imperial Dragons", for Pathfinder) Planar Dragons, and Epic Dragons.
In an expansion of the alignment mechanic, chromatics helped define what our frenemies on TVTropes calls "Color Coded For Your Convenience", where the general color-scheme of a dragon immediately helps you figure out what they are as a general rule.
Chromatic Dragons are always based on "plain" colors, and are usually portrayed as Evil aligned in various different ways depending on the precise breed. Their associated patron goddess is Tiamat, who materializes as a gargantuan she-dragon with five heads, corresponding to the five most iconic breeds of Chromatic Dragon.
They uniquely unlike metallics are more likely to breed between species(of chromatics) and create mules as shown in dragon magazine #65 and #248 which have mixtures between the breathtypes when its chromatics. and a light mention in 3e draconomicon as crossbreeds. And.. dragons can crossbreed with pretty much anything heck there was a bear dragon in an ashardalon campaign. Now i know your wondering does this mean dragons can crossbreed with other dragon types(i.e chromatic+metallic) The answer is yes but the child is usually viewed as an abbaration and hunted down.But it is possible for a dragon to care for it but thats extremely rare each dragon is unique after all.
Chromatic dragons can learn polymorph if they work for it unlike the metallics who get it naturally or any spell really heck even dragons have their own spells they can learn.
The Original 5
Black Dragons favor swampy lairs where they can lie in ambush crocodile-style, since they can breath underwater. They are also known as "skull dragons" for their skeletal facial features. They tend to be described as particularly cruel and sadistic, even by dragon standards. They wield gouts of acid slime as a breath weapon.
Blue Dragons are iconic for their single enormous snout-tip horn, like a rhino's. Using powerful blasts of lightning breath to vaporize foes, they are traditionally considered denizens of the desert - which many fans find a little weird, given they are, y'know, bright freaking blue. They have the ability to flat out destroy water. Unusually this ability is exclusive to them, yet the ability to create indefinitely lasting water from nothing is everywhere. 4th edition made them prefer coastal regions and other places where storms are common, instead. They are traditionally portrayed as amongst the most reasonable and least malevolent of the Chromatics; show them respect, and they'll usually leave you alone. In 5th edition, they're back to living in deserts and dry steppes.
Favoring forest environments, Green Dragons are characterized as manipulators and head-gamers par excellence. These dragons had it kind of rough in 3rd edition; with the change to poison rules in that edition, their traditional breath weapon, a gout of poisonous vapor, no longer worked, so they were forced to use corrosive fumes and do acid damage instead. They went back to poison after 3rd edition.
In Pathfinder they're actually decently likely (possibly 1 in 10, but likely lower) to be neutrally aligned. This is largely a result of them being too lost in their books to care about being evil.
The most iconic and traditional of all D&D dragons, Red Dragons are arrogant, greedy, hot-tempered, flame-spewing, power-hungry, malevolent brutes who enjoy eating maidens.
Smallest and weakest of their kind, White Dragons are feral and savage, notably inferior in intelligence to the other Chromatic breeds (that doesn't mean they are stupid though, they just don't like to use their brains that much). Their icy breath weapon is nothing to sneeze at, though. They even use it to encase their hoard and trophies in ice so that they can decorate their lair. It also makes it pretty difficult for potential thieves to come and grab something, as they first have to break the ice to get to the stuff, at risk of having the dragon return and add the said thieves to its frozen collection. Crystal dragons are known to take their eggs and raise them to make them less evil; this may result in a white dragon that uses its brain more and defies the stereotype.
Other Chromatic Dragons
The Realms version debuted in Advanced Dungeons & Dragons 2nd edition, in the Monstrous Compendium Appendix: Forgotten Realms splatbook, before making it on to the Monstrous Manual. This dragon, also known as the "Great Desert Dragon", is a flightless burrowing dragon that inhabits the desert regions of the Realms, namely Raurin and Eastern Mulhorand, where it competes with the better-known Blue Dragon for prey. Armed with an acidic spray, these Brown Dragons prefer to dig themselves into the sands and then launch themselves at any edible creature that gets nearby. Their favorite food is horseflesh. It's noted that the natives of the deserts have a peculiar respect for these dragons, so they often describe them as less evil than their Blue Dragon rivals. It may be because Brown Dragons have little interest outside of being apex predators and are freely hunted by the natives, whilst Blue Dragons are more inclined to setting themselves up as overlords reigning over human slaves.
The World Axis version is, of course, unique to Dungeons & Dragons 4th Edition, appearing in the Chromatic Draconomicon. This version possesses distinctive sail-like frills down its sides and is capable of flight, although they are much better at burrowing. Also known as "Sand Dragons", these Brown Dragons are largely disinterested in the idea of ruling over anything; their most predominant trait is that they are gourmet epicures. Their love of food and cooking skills is so great that a Brown Dragon's hoard is often based on a mixture of exotic animals, long-forgotten (and thus highly valuable!) cook books, cooking utensils made out of fabulously expensive materials, rare spices, precious wines and liquors... basically, Sand Dragons are the only dragons who would earn an entry in the Great Book of Grudges for carrying off barrels of Bugman's XXXXXXXX and enslaving dwarven brewers. Best characterized as hedonists, 4e Brown Dragons only care about living a life of ease and comfort, and so they actively prefer to avoid stirring up trouble with humanoids - raiding a farmer's flocks every now and then is much less hassle than demanding human sacrifices from a neighboring village. These Brown Dragons have a breath weapon made of high-velocity sand gouts, which can scour flesh from bone.
Uniquely amongst the chromatic dragons, gray dragons are only found in the Nentir Vale setting, having been invented for Dungeons & Dragons 4th Edition and appearing in the Chromatic Draconomicon. They are, however, based on an older dragon; the Fang Dragon. They don't even try to hide this fact; their literal in-game lore is that Tiamat created Fang Dragons, found them to be disappointments, and so tried to improve the breed. She took a clutch of Fang Dragon eggs, infused them with medusa blood, then had a basilisk brood them in a nest made of cockatrice feathers for a year. When they hatched, they had gained the ability to both petrify creatures with their touch and to spew a caustic slime that quickly dried into a stone-hard substance. Impressed with the results, she set them to hunting down their former relatives, and thus there are few if any Fang Dragons left to be found in the Nentir Vale world.
Personality-wise, gray dragons - also known as Stone or Spike Dragons, and sometimes referred to as Fang Dragons by those who confuse them with their ancestors - can be best summarized as "White Dragon 2.0". They're not stupid, but they are rapacious, venal, brutish, fickle, voracious predators absolutely obsessed with hunting. A gray dragon not only thinks it's the biggest, meanest predator around, it wants to prove it, so their diet is largely made up of humanoids and monsters, because these pose an actual challenge to bring down and eat.
Gray Dragons inhabit rocky badlands and border-regions, where they typically have both a central "lair", where they keep their hoards, and multiple "outposts", which they migrate between as they scour their territory for prey.
The term "Gray Dragon" was used prior to this monster, however, as a specific breed of Linnorm.
Orange Dragons have only appeared in one format, unlike almost every other dragon on this list, which is a rather sad form of uniqueness. They debuted in Dragon Magazine #65 alongside the Yellow and Purple Dragons in the article "The Missing Dragons" for Advanced Dungeons & Dragons 1st edition. In this source, they were described as a "secondary chromatic", the result of crossbreeding between two other breeds of chromatic dragon - in this case, the Red and Yellow Dragons. Like most 1e monsters, there wasn't a lot of lore to them; basically, all we're told is that they love to hunt in and near water, inhabiting cave systems adjacent to swamps, rivers, and lakes, they tend to hunt at night to compensate for their glaring color scheme, and their breath weapon is a gout of liquid sodium... basically, clinging fire that explodes if it touches water.
The Orange Dragon was subsequently updated to AD&D 2nd edition in Dragon Magazine #248: "The Return of the Missing Dragons". Now also known as "Sodium Dragons", they are stated to only inhabit the riverbanks and lake shores of steamy tropical rainforests, where the abundant moisture keeps their sodium breath weapon from going too out of control. They are excellent swimmers, but unlike other water-loving dragons have no inherent water-breathing abilities. Black dragons keep out of their way, as orange dragons are bigger, stronger, and much nastier, but there is a bitter rivalry between orange and bronze dragons.
There are two distinct kinds of Purple Dragon - three, if one considers the Deep Dragon to be the Forgotten Realms version of the Purple Dragon. Which is a reasonable assumption to make, considering... but we'll get to that.
The Purple Dragon first debuted in Dragon Magazine #65 alongside the Yellow and Orange Dragons in the article "The Missing Dragons" for Advanced Dungeons & Dragons 1st edition. In this source, the Purple Dragon was described as a "secondary chromatic", a subspecies of dragon created by the crossbreeding of Red and Blue Dragons. As these were the two most powerful Chromatic Dragons, the Purple Dragon was the most powerful of the secondary chromatics. Very little lore is actually presented about this prototype Purple Dragon, save that they breath an explosive plasma blast (a hybrid of the fire and lightning breaths of their ancestors), and they tend to favor deep cavern lairs, including in what would become the Underdark.
This purple dragon was subsequently updated to AD&D 2nd edition in Dragon Magazine #248: "The Return of the Missing Dragons". Now also known as "Energy Dragons", they were still suspected to be the product of Red and Blue Dragon crossbreeding, but they also gained a new potential origin as the children of a lost member of the Dragon Gods, a sister to Tiamat whom she destroyed. This version of the purple dragon has a lot more fluff than its 1e predecessor. Energy dragons are characterized as the most sinister, evil and sadistic of all the Chromatics. Favoring deep cavern and Underdark lairs, they prefer to emerge from the depths to hunt prairies, plains, and low foothills, preferably at night and/or in the middle of a fierce thunderstorm - not because they have any sensitivity to light, but because these dark conditions amplify the terror of their raids. They favor meat, but will begrudgingly supplement their diet with tuberous vegetables such as potatoes, onions and carrots if they must, but this makes them even meaner. They still spit plasma, but now they can do so in three forms; a diffuse cloud, a more focused conical blast, or a tightly focused scything "blade" of energy.
In the Nentir Vale, a different kind of purple dragon can be found, invented for Dungeons & Dragons 4th Edition and appearing in the Chromatic Draconomicon. This version, however, is largely based on the Deep Dragon of the Forgotten Realms, being an Underdark-dwelling serpentine species rarely seen on the surface. However, it also has its own unique quirks; the World Axis purple dragon is an inveterate explorer and loves nothing more than to spelunk into new territories - wandering around the Underdark and exploring new places is a genuine delight for them, and they are notably less sadistic and manipulative than their counterparts from other planes and editions. They possess a breath weapon unique to them; clouds of psychotropic venom that cause Psychic damage, and also have the unique ability to turn into insubstantial shadows.
Similarly to the Steel Dragon, the Yellow Dragon is a Chromatic with a somewhat convoluted history, with different appearances in different settings and different editions.
The original Yellow Dragon appeared in Advanced Dungeons & Dragons 1st edition in the article "The Missing Dragons", for Dragon Magazine #65. Here, they shared the limelight with the Purple and Orange Dragons. Unlike them, though, the yellow dragon was characterized as a "missing Primary Chromatic", the ancestor of the Green and newly introduced Orange Dragons. Very little lore is provided for this Yellow Dragon, save that they can spit sprays of salt crystals and they favor lairs along oceanic coasts and amongst salt flats.
This version of the Yellow Dragon would be updated to 2e in the article "The Return of the Missing Dragons" in Dragon Magazine #248. Like its purple and orange counterparts, this version underwent a major lore expansion. Now known as "Salt Dragons", and with a graphic redesign from a fairly generic dragon in #65 to a more "giant snake with dragon legs" look, this 2e Yellow Dragon was characterized as a vicious, sadistic ambush hunter that dwelled in seashores, salt marshes, salt flats and inland seas. They often cooperate with sahuagin or any other race that is willing to live in the same area. They still spray blinding gouts of salt and can produce green and orange dragon offspring through crossbreeding. A new bit of lore here is that yellow dragons may be connected to a slain sister-goddess of Tiamat.
Whilst this was going on, another form of Yellow Dragon was taking shape over in the Forgotten Realms. Debuting in the original Draconomicon, the Faerunian yellow dragon is a desert-dwelling breed that clashes with the blue and brown dragons. Able to expel high-velocity, scorching hot wind laced with flesh-scouring sand, they are burrowing ambush predators, specifically favoring the antlion tactic of "dig a deep pit, lurk at the bottom, eat anything that falls in. They are hyper-territorial isolationists, refusing to tolerate each other except during the mating season. These dragons actually made it into the Monstrous Manual, alongside the brown dragon and the Deep Dragon, which is something that can't be said for the Dragon Magazine chromatics.
Yellow dragons haven't been seen since the days of AD&D. Not even Monsters of Faerun, which revived the Brown Dragon, Deep Dragon, Fang Dragon, Shadow Dragon, and Weredragon (under the name Song Dragon), brought them back.