From Lexicanum

Typical Warrior	Basic Data		Rune Symbol
	Name	Arach-Qin
	Main colours	Black, purple helmet, red faceplate, beige details

Arach-Qin is an Eldar Craftworld. Little is known about Arach-Qin, other than its existence. It is most likely an extremely minor Craftworld.

Source

• The Colours of the Craftworlds (UK GW website)