What do the colours of the Japan flag mean?

White: honesty and purity. Crimson: the sun, and sincerity and warmth.

How do you tell the Japan flag from the Bangladesh one?

Bangladesh has a green field and its red disc is deliberately off-centre toward the hoist. Japan's field is white and its disc is centred.

When was the Japan flag adopted?

The current design dates from 1870, and its official ratio is 2:3.

The flag of Japan

A plain white field with a large crimson disc at the exact centre, three-fifths of the flag's height across.

Ratio 2:3 · current design adopted 1870

Japan

The design is centuries older than its legal status: the Hinomaru appears on war fans and temple banners from the medieval period, was designated for merchant ships in 1870, and only became the legal national flag in August 1999. That 1999 act changed two things — it set the ratio at 2:3 rather than 7:10, and it moved the disc to the exact centre. Under the 1870 regulation the disc sat one-hundredth of the flag's length toward the hoist, an optical correction so it would look centred on a flag hanging from a pole. The red is specified as a shade of crimson rather than pure red, though flags flown in practice vary considerably.

Flags it gets confused with

Japan

Bangladesh

Palau

Drawn at each flag’s own official ratio, which is itself the difference in some of these pairs.

Flag	How to tell them apart
Bangladesh	Bangladesh has a green field and its red disc is deliberately off-centre toward the hoist. Japan's field is white and its disc is centred.
Palau	Palau's field is light blue and its disc is yellow and off-centre — and it represents the moon, not the sun.

What the colours mean

Flag laws usually specify a Pantone chip, a CMYK mix or just a colour name. Converting any of those to sRGB is lossy, which is why published hex values disagree.

The symbols on it

What	What it stands for
Red disc	The sun, from the country's name — Nihon, "origin of the sun"

Ratio: 2:3
Current design adopted: 1870
Colours: white, crimson

Common questions

What does the flag of Japan look like?: A plain white field with a large crimson disc at the exact centre, three-fifths of the flag's height across.
What do the colours of the Japan flag mean?: White: honesty and purity. Crimson: the sun, and sincerity and warmth.
How do you tell the Japan flag from the Bangladesh one?: Bangladesh has a green field and its red disc is deliberately off-centre toward the hoist. Japan's field is white and its disc is centred.
When was the Japan flag adopted?: The current design dates from 1870, and its official ratio is 2:3.

Japan Capital, area, population and currency
The flag of Bangladesh Routinely mistaken for this one
The flag of Palau Routinely mistaken for this one
Every flag with white in it
The flag of United States Ratio 10:19
The flag of India Ratio 2:3
The flag of United Kingdom Ratio 1:2
The flag of Canada Ratio 1:2
The flag of France Ratio 2:3
The flag of Russia Ratio 2:3
The flag of Brazil Ratio 7:10
The flag of Italy Ratio 2:3

Sources

Official vendor product documentation — At One Place

How these figures are compiled and checked