Tokyo is a city with two flags, and neither one is a mistake. The first is a field of deep Edo purple with a white six-rayed sun at its center, adopted in 1964 and still the official flag of the Tokyo Metropolis. The second is white with a green mark that manages to be a ginkgo leaf and a letter T at the same time, adopted in 1989 as the everyday face of the metropolitan government. Formal occasions get the purple flag. Buses, trains, buildings, and paperwork get the green one. Visitors who notice both often assume one replaced the other; in fact they are co-workers with different shifts.
The purple flag of 1964
The metropolitan flag was adopted on October 1, 1964, nine days before the opening ceremony of the Tokyo Olympic Games. The timing was no accident of the calendar: the city was about to present itself to the world in its first turn as Olympic host, and it went into the fortnight with a flag of its own.
The field is Edo purple, Edo murasaki, a deep bluish purple named for the dye tradition of Edo, the shogunal capital that was renamed Tokyo in 1868. Murasaki is the Japanese name of the gromwell plant whose roots yielded the dye, and the Edo variant of the color, bluer than the older purples of Kyoto, was a fashion of the Edo period, associated with the city's dyers and with kabuki costume. Putting it on the flag connects the modern metropolis to the older city underneath. There is no single fixed digital value; reproductions commonly land near indigo, around #4b0082. The flag's proportions are 2:3, and the crest sits in white at the center.
A crest older than the Metropolis
The white emblem on the flag is the metropolitan crest, and it is much older than 1964. Designed by Hiromoto Watanabe, it was approved by the Tokyo City council in December 1889, the year the modern municipality of Tokyo City was organized. When wartime reorganization abolished Tokyo City and merged it with Tokyo Prefecture to form the Tokyo Metropolis, the new government kept the old city's emblem, formally adopting it on November 2, 1943.
The design is a sun: a central disk with six rays spreading outward, drawn so evenly that many people read it first as a snowflake or a compass rose. The official reading is Tokyo as the center of Japan, the point from which energy radiates. It is hard to miss the conversation with the national flag, which is nothing but a red sun disk on white. Japan's flag shows the sun; Tokyo's crest claims the capital as the place the sun shines from. As civic self-confidence goes, an 1889 city council rarely put it more compactly.
The green symbol of 1989
A century after the crest, the metropolitan government decided it also needed something friendlier. In 1989 it ran a selection process for a new symbol, reviewed 20 candidates, and on June 1 adopted a design by Rei Yoshimura, a professional graphic designer. Three green arcs curve together into the silhouette of a ginkgo leaf, and, squinted at another way, a capital T for Tokyo. The ginkgo is Tokyo's official metropolitan tree, the species that lines Meiji Jingu Gaien's famous avenue and turns the city yellow every November, so the leaf was not an arbitrary choice. The official color is a bright shade the government calls vivid green.
On September 30, 1989, Tokyo adopted a flag to carry the new mark: the green symbol centered on a white field. This is the symbol flag, and it is the one modern Tokyo actually wraps itself in. It flies at metropolitan government buildings, rides on Toei buses and subway cars, and fronts the government's publications and website.
Which flag is official?
Both, which is the part that confuses people. The 1964 purple flag remains the official flag of the Tokyo Metropolis and does the ceremonial work; the 1989 symbol flag has official standing of its own and does nearly everything else. The arrangement resembles a company that keeps its founding seal for contracts while using a modern logo on the storefront, except that in Tokyo's case both the seal and the logo are flags.
Neither flag carries text, a seal, or more than two colors, which puts both comfortably within the design rules vexillologists usually have to beg governments to follow. The practical result of the division of labor is that the purple flag, though senior, is the rarer sight. Spotting it generally means you are looking at a formal metropolitan occasion, an assembly hall, or a protocol lineup of prefectural flags, where each of Japan's 47 prefectures flies its own emblem-on-solid-color banner and Tokyo's Edo purple sits among them. The green flag, meanwhile, is simply part of the street furniture of the city, so common it goes unnoticed.
References
[1] "Symbols of Tokyo," Wikipedia. https://en.wikipedia.org/wiki/Symbols_of_Tokyo
[2] "Flag of Tokyo," Simple English Wikipedia. https://simple.wikipedia.org/wiki/Flag_of_Tokyo
[3] "Tokyo (metropolitan area) Flag," Flags and Anthems. https://www.flags-and-anthems.com/city/flag-tokyo-metropolitan-region.html