As of version 5.1.0, the glowing dragon's breath type and resistances are randomized, along with all other dragon colors (except the chromatic dragon).
In the West the dragon was the natural enemy of man. Although
preferring to live in bleak and desolate regions, whenever it
was seen among men it left in its wake a trail of destruction
and disease. Yet any attempt to slay this beast was a perilous
undertaking. For the dragon's assailant had to contend
not only with clouds of sulphurous fumes pouring from its fire
breathing nostrils, but also with the thrashings of its tail,
the most deadly part of its serpent-like body.
[ Mythical Beasts by Deirdre Headon (The Leprechaun Library) ]
"One whom the dragons will speak with," he said, "that is a
dragonlord, or at least that is the center of the matter. It's
not a trick of mastering the dragons, as most people think.
Dragons have no masters. The question is always the same, with
a dragon: will he talk to you or will he eat you? If you can
count upon his doing the former, and not doing the latter, why
then you're a dragonlord."
[ The Tombs of Atuan, by Ursula K. Le Guin ]