What is the seventh clan? In the first season of K, we're introduced to the red, blue, and colorless clans early on, and later on are told about the silver and gold clans. In the movie, we come to know of the green clan.

But there are seven clans, and that only amounts to six. What is the color (or non-color?) of the seventh clan?
From the first to last clans, they are White Rice Party, Tokijikuin, Homra, Scepter 4, Jungle, Cathedral, and Colorless. Cathedral was COMPLETELY destroyed in the kagutsu crater incident, therefore the only one in the series that has any resemblance to the powers of the Gray clan, is the Gray King Seigo Ootori. (Tenkei Iwafune) And any sort of information given on Cathedral is little to null on even the Wikipedia, other than the interesting insignia of their clan.