The chromatic dragons are probably the most infamous of the two kinds of dragons people are likely to encounter in Dungeons & Dragons (and many of its variants and derivatives).
As the name implies, the chromatic dragons are colorful, to wit, each type of chromatic dragon is principally colored with one color, and together, they form a whole rainbow. Of course, the chromatic dragons have reputation of being quite competitive, and as such getting them in a single group portrait requires either some travelling from the artist's part, very daring bravery, or some Arcane Magic (for example, the transposition/transmutation spell 'Biowarium toolkittus Aurora Neverwinterum nocturnalis', popular among the young magicians, with the older magicians studying its use with great interest as well).
Chromatic dragons are evil by nature. All dragons are dangerous when annoyed, and chromatic dragons can also be very dangerous when they are not particularly annoyed, and a dangerous degree of annoyance can often be arranged easily enough (With lifespans of thousands and thousands of years, they get to hear same old jokes all over again far too many times, especially that "got a light?" thing...) However, people have walked in a dragon's cave and lived to tell the tale, and, knowing the legendary amounts of wealth dragons have in their lairs (most dragons, by nature, tend to collect things, most preferrably valuable things), some even arrange profitable business deals. Of course, it is not usually these people who get most of the profit, but getting charred by a partner is a symptom of an unsound business decision.
Chromatic dragons are intelligent, however, and often ready to negotiate, even when they have the tendency to get what they want, and tend to get rid of potential threats very easily. There are people who mistakenly believe that only mighty red wyrms are intelligent, and that white dragons are "stupid". This is misleading. White dragons are comparatively rather stupid, but compared to most ordinary mortals, they can be quite brilliant. All adult dragons of any sort are quite smart already, easily match to most humans.
While dragons of same color often - but not always - tend to get along, many dragon types do not react well to each other. And, I'm fairly sure, none of them particularly values the metallic dragons, the good and noble branch of the dragon family.
The Dungeons and Dragons 3rd Edition recognizes following chromatic dragon types:
- White dragons, the predatory, ice-breathing, not always brightest ones from cold parts of the world.
- Green dragons, aggressive acid-breathers,
- Black dragons, acid-breathing cunning ones,
- Blue dragons, vain and territorial desert wyrms, breathing lightning, and
- Red dragons, the fire-breathing ones, the fiercest and most famed of them all, covetuous and vain.
(Source: D&D3e Monster Manual and the SRD Monsters section.)
In Nethack, there is also The Chromatic Dragon, known better to most people with its other name, Tiamat. The Chromatic Dragon is the quest nemesis of the Caveman character class. Gorgonzola tells me the beast in this form comes from AD&D.
The Chromatic Dragon is a 16 hit dice monster. It is resistant to all special attacks, and has 30% magic resistance. It has a breath weapon attack, Magic missile attack, a steal attack, and 3 other attacks, which - in non-gamer terms - means it's quite lethal. (Good that Cavemen are not blessed with great intelligence or weapons more formidable than a club and a sling... reckless, blissfully ignorant bravery is just what legends are made of.)
When I was a kid, I had this odd dream where I got to the Tiamat's Lair and fought the dragon... the next day I started the game up in the Wizard Mode and did that. It was difficult, even when I couldn't die, and in the end, I felt nothing. I guess it's a sign that I should never fight the dragons.
(Source: Dylan O'Donnell's Nethack 3.4.0 spoiler files.)