User blog comment:B214/High School DxD EX/@comment-50.139.232.230-20151110031112/@comment-1359322-20151110043410

Well most of the child seem to be referenced after the parents in some way.


 * Kurenai - Crimson (Ise, Rias, Akeno's Ake = scarlet/vermilion)
 * Zen - Slash (Mother)
 * EX (イクス) - Taken from his mother's signature move Extinguished Star ( イクス ティングイッシュ・スター)
 * Kurobara - Black
 * Shirayuki - White

Of course only Airi is named based on the names, but Kurenai's name is also a good example especially since Ise, Rias & Akeno has red related to them in some form.