Chromatic dragon (UnNetHack)
UnNetHack includes generic chromatic dragons, in addition to the Chromatic Dragon who serves as the Cave(wo)man quest nemesis of vanilla. That unique monster still plays the same role in UnNetHack, but has been renamed "Tiamat" (her name according to the in-game encyclopedia) to avoid ambiguity.
Chromatic dragons share the same assortment of breath attacks and resistances as Tiamat but are otherwise somewhat weaker opponents. They have a lower difficulty level and lack Tiamat's spellcasting and sting attacks.
Although chromatic dragons are not considered unique monsters, they are not randomly generated. They are only found at the bottom of the Dragon Caves, a new branch added to Gehennom in UnNetHack, where several are guaranteed to appear in a lair.
UnNetHack does not include baby chromatic dragons. Chromatic dragon eggs will hatch into fully grown dragons.
Chromatic dragons' key significance to players is that when they are killed they may leave chromatic dragon scales, which may be enchanted into chromatic dragon scale mail. Chromatic dragon scales confer the resistances of every color of dragon scale mail, including petrification resistance (conferred by the 'stone dragon', which as of version 5.1.0 has a randomized name) and reflection.
In earlier versions players could (attempt to) acquire chromatic dragon scales without entering the Dragon Caves by a wish for one or more chromatic dragon eggs. This option was eliminated in development version r1580, which prohibits wishing for chromatic dragon eggs. (Chromatic dragons are not valid polymorph options, so players cannot polymorph into one in order to lay eggs.)
Fearsome dragons who are channeling the powers of lesser dragons
like their mother Tiamat. Legends tell of a far away realm where
these creatures can be found in large numbers.