What do the colours of the Singapore flag mean?

Red: universal brotherhood and the equality of man. White: pervading and everlasting purity and virtue.

How do you tell the Singapore flag from the Indonesia one?

Indonesia is plain red over white with no crescent or stars.

When was the Singapore flag adopted?

The current design dates from 1959, and its official ratio is 2:3.

The flag of Singapore

A red band over a white band, with a white crescent and five white five-pointed stars arranged in a circle in the upper hoist.

Ratio 2:3 · current design adopted 1959

The crescent is explicitly a waxing moon standing for a young country, not a religious emblem, and the five stars name five ideals rather than states or provinces — the symbolism was chosen to be acceptable to every community at once. Singaporean law is unusually detailed about display: the flag may not be used on anything that touches the ground, and permission is needed to display it outside the National Day period. The design is red over white, which inverts Indonesia's and matches Poland's order. It was adopted in December 1959, six years before full independence.

Flags it gets confused with

Indonesia

Poland

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

Flag	How to tell them apart
Indonesia	Indonesia is plain red over white with no crescent or stars.
Poland	Poland is white over red and has no emblem.

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
Crescent	A young nation on the rise
Five stars	Democracy, peace, progress, justice and equality

Ratio: 2:3
Current design adopted: 1959
Colours: red, white

Common questions

What does the flag of Singapore look like?: A red band over a white band, with a white crescent and five white five-pointed stars arranged in a circle in the upper hoist.
What do the colours of the Singapore flag mean?: Red: universal brotherhood and the equality of man. White: pervading and everlasting purity and virtue.
How do you tell the Singapore flag from the Indonesia one?: Indonesia is plain red over white with no crescent or stars.
When was the Singapore flag adopted?: The current design dates from 1959, and its official ratio is 2:3.

Singapore Capital, area, population and currency
The flag of Indonesia Routinely mistaken for this one
The flag of Poland Routinely mistaken for this one
Every flag with red in it
The flag of United States Ratio 10:19
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 China Ratio 2:3
The flag of Germany Ratio 3:5
The flag of Russia Ratio 2:3
The flag of Italy Ratio 2:3

Sources

The World Factbook — Central Intelligence Agency (Public domain (US Government))

How these figures are compiled and checked