Why does the Japan soccer team wear blue despite their red-and-white flag? The official answer from the Japan Football Association describes:
Although it is said that the blue is symbolizing the sea and sky surrounding Japan islands, in fact it is retrospective reasoning. There is no reliable document proving the reason why it is blue. Japan’s national team uniform was blue at the first half of the 20th century, and it continues to the present day.
Japan Football Museum exhibits the oldest national team’s shirt in existence looking light blue. There is no evidence older than that. The only thing that we can do is guess.
The blue presumably being the colour of college sports
The best guess at the moment is that the blue is coming from college sports. After the Meiji Restoration (1868), football was played by students of colleges, universities, and (especially) normal schools in Japan. The emperor’s cup was monopolized by students’ teams until 1959.
In the Meiji era, Japanese society wanted to learn everything from western nations, regardless of its importance. When the first boat race between the university of Tokyo and Kyoto was held, they put on blue shirts to imitate boat race between the university of Oxford and Cambridge. After that, other sports teams at the University of Tokyo have tended to wear light blue shirt. Soccer team of the university also did so.
International sports games started at the end of the 19th century. For a decade, there was no systematic method to nominate members of a national team. Sometimes “representative” (代表, Daihyō) method was applied: the winner of a domestic tournament directly became a national team. For example, the first national team was the team of the Tokyo Higher Normal School itself. In other cases, “selection” (選抜, Senbatsu; cf. Seleção of Brasil) method was used: member of the national team was picked up from several teams joining domestic tournaments. Both methods coexisted for several decades.
In 1930, Japan national soccer team for the 9th Far Eastern Games was nominated by “representative” method. The team was mainly consisted of the students from the university of Tokyo, who wore blue shirts in domestic tournaments. It is guessed that they kept wearing blue shirts at the national team.
Members for the 1936 Olympic Games were nominated by “selection” method. The members did not have common shirt because they are selected from various teams in domestic tournament. As a results, the team took over blue shirts from former national team. Finally, those blue shirts became the oldest national team’s jerseys in existence.
This is the storyline of a leading hypothesis for the colour of the Japan national soccer team. Although the centre of Japanese football was shifted from amateur to professional since 1993, national team continues wearing blue shirt. These days the blue became darker.
It is said that the colour of the boat race team, light blue, originates from the colour of Eton College where the association football begun. The samurai’s blue shirts are the legacy of football’s college sport era.