Apocanon (Abyssal) from Servants of the Betrayer Deck
Abyssals are demonic constructs similar to infernals, but made from rougher, more jagged material, and burn with a red flame instead of a green one. Certain abyssals, including Supremus who serves Illidan Stormrage in the Black Temple, glow with a blue flame as well.
This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials. It should not be taken as representing official lore.
The differences in the colour of the flames of Infernals, Abyssals and Supremus could be tied to what sort of elemental was bound within. Perhaps Abyssals are created from more powerful elementals and Supremus from an even more powerful elemental.