Nightlight

Luminous dragons (A species I made up) Are known for giving off a bright light in dark areas, some use them as escorts to dark caves or traveling at night, Smaller versions of the species are kept as house pets to light up the rooms of small children scared of the dark(they had earned the name night lights) 

Under normal circumstances, luminous dragons are bright colors like white, gold or yellow. In the case of Night, they are dark green apart from their eyes and the tuft on their tail, to compensate for this their eyes and tail glow brighter since their body doesn't glow very bright. Night is also a small dragon being about the size of an adult lynx compared to ones that are the size of a grown horse. They use magic to change their shape and either appear bigger or alter their form entirely.