Primordial

Primordials (原初の悪魔 gensho no akuma, lit. "Primordial of Demon") also known as Progenitors or Primals, are the oldest and most extraordinarily powerful Demons. Each of them is referred to by their signature colors rather than an actual name.

These "substitute names" don't count as their actual names in the true sense of being a named monster:
 * Purple Primordial Violet
 * White Primordial Blanc ("Blanc")
 * Yellow Primordial Jaune
 * Black Primordial Noir (Nero)
 * Green Primordial Vert
 * Blue Primordial Bleu
 * Red Primordial Rouge (Feuer)