The file
Cookies as cereal, officially. Oreo O's turned the milk gray-brown and tasted exactly like the cookie, which was the entire pitch and the entire appeal.
A corporate split between Post and Kraft meant Post lost the rights in 2007, and the cereal survived only in South Korea, where Americans were paying to import it. The rights were sorted out and it came back to U.S. shelves in 2017.
Back on shelves. The milk still goes gray.
Sources: Wikipedia — Oreo O's