What do the colours of the Vietnam flag mean?

Red: revolution, and the blood of the struggle for independence. Yellow: the star; the traditional colour of the Vietnamese people.

How do you tell the Vietnam flag from the Morocco one?

Morocco's star is a green interlaced outline, not a solid yellow star.

When was the Vietnam flag adopted?

The current design dates from 1955, and its official ratio is 2:3.

The flag of Vietnam

A red field with a large five-pointed yellow star at the centre.

Ratio 2:3 · current design adopted 1955

The star's points were rounded slightly in 1955, which is the only design change since the flag first appeared in 1940 — the earlier version had blunter points. It is one of the simplest national flags and one of the easiest to confuse with Morocco's and China's at speed. The five-point symbolism of social classes parallels the four small stars on the Chinese flag without copying them. Vietnamese law does not specify a Pantone value, and reproductions vary between a scarlet and a deeper red.

Flags it gets confused with

Flag	How to tell them apart
Morocco	Morocco's star is a green interlaced outline, not a solid yellow star.
China	China has five stars in the upper hoist, not one in the centre.

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
Five-pointed star	The five groups of society: workers, peasants, soldiers, intellectuals and traders

Ratio: 2:3
Current design adopted: 1955
Colours: red, yellow

Common questions

What does the flag of Vietnam look like?: A red field with a large five-pointed yellow star at the centre.
What do the colours of the Vietnam flag mean?: Red: revolution, and the blood of the struggle for independence. Yellow: the star; the traditional colour of the Vietnamese people.
How do you tell the Vietnam flag from the Morocco one?: Morocco's star is a green interlaced outline, not a solid yellow star.
When was the Vietnam flag adopted?: The current design dates from 1955, and its official ratio is 2:3.

Vietnam Capital, area, population and currency
The flag of Morocco Routinely mistaken for this one
The flag of China 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 Germany Ratio 3:5
The flag of Russia Ratio 2:3
The flag of Italy Ratio 2:3
The flag of Mexico Ratio 4:7

Sources

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

How these figures are compiled and checked