The Yamanote Line is currently celebrating 100 years since its naming. The original portion of the Yamanote Line was built in 1885 between Shinagawa and Akabane called the Shinagawa Line, passing through areas such as Tokyo station, Akihabara and Ueno.
The top part of the loop stretching between Ikebukuro and Tabata, completed in 1903 was called the Toshima line, 豊島線.
In 1909 after the line was turned into an electric one, both lines were merged and called the Yamanote Line.
In 1925 the line between Kanda and Akihabara was opened for the Yamanote Line and the loop was completed.
To celebrate the 100 years, JR has wrapped one of its trains in the original brown, ‘chocolate’ colors. I say chocolate because Meiji Chocolate has managed to feature its products on the trains wrap, which makes you wonder whether this is just really celebrating the 100 years or just an excuse to collect some more revenue through advertising.
Someone has made a video and put in on YouTube also