This is from my personal research on the topic that was originally published in 2015.
1884, New Years Celebration: Jigoro Kano Introduced Dankyuisei (Dan and Kyu system) to martial arts.
1886, October: Jigoro Kano Introduces Black Belt for Yudansha after the Kodokan Grows to 130+ students. Later the same year he introduced the White Belt for Mudansha.
1924, April: Karate adopts the Dankyuisei, Dōgi, and Obi for the first time, when Gichin Funakoshi awards six Shodan and one Nidan to his students.
1930: Kohaku Obi (Crimson and White Belt) introduced by Jigoro Kano to represent Kodansha, and is considered optional.
1937: Colored Belts introduced by Mikinosuke Kawaishi in Europe. Original system relied on dying the same belt multiple times, and the original color scheme was White, Yellow, Green, Blue, Purple, and Brown, with students getting a new Black Belt when they became a Yudansha. This system was rejected by most Japanese.
1943: Aka Obi (Red Belt) introduced to represent 9th and 10th dan in Judo.
1943-1945: Belt System introduced to Korea via Karate.
1945: Karate’s rank system goes from maxing at 5th dan to maxing at 10th dan.
1959: Youngest legitimately awarded 10th dan goes to Eizo Shimabukuro, who was 34 at the time.
1965: Okinawan Karateka have a meeting to establish time-in-rank and age requirements for Yudansha for the first time. Title Stripe System was introduced via Okinawan Karate-ka.