What do the colours of the Vatican City flag mean?

Gold: the golden key of spiritual authority. White: the silver key of temporal authority.

How do you tell the Vatican City flag from the Switzerland one?

The other square flag, but plain red with a white cross and no emblem.

When was the Vatican City flag adopted?

The current design dates from 1929, and its official ratio is 1:1.

The flag of Vatican City

A square flag divided vertically, gold at the hoist and white at the fly, with the crossed keys of St Peter and the papal tiara on the white half.

Ratio 1:1 · current design adopted 1929

Vatican City

One of two square national flags, adopted with the Lateran Treaty of 1929 that created the Vatican City State. The colours come from the cockade of the papal army after 1808, when gold and white replaced the earlier yellow and red. The keys are always shown crossed with the gold one pointing up to the viewer's right; getting them the wrong way round reverses the theology. The tiara stayed on the flag even after Paul VI set his own aside in 1964, so the flag depicts an object that is now a museum piece.

Flags it gets confused with

Vatican City

Switzerland

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

Flag	How to tell them apart
Switzerland	The other square flag, but plain red with a white cross and 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
Gold key	Spiritual power — the power to bind and loose in heaven
Silver key	Temporal power on earth
Papal tiara	The three-tiered crown of the pope, retained on the flag though no pope has worn one since 1963

Ratio: 1:1
Current design adopted: 1929
Colours: gold, white

Common questions

What does the flag of Vatican City look like?: A square flag divided vertically, gold at the hoist and white at the fly, with the crossed keys of St Peter and the papal tiara on the white half.
What do the colours of the Vatican City flag mean?: Gold: the golden key of spiritual authority. White: the silver key of temporal authority.
How do you tell the Vatican City flag from the Switzerland one?: The other square flag, but plain red with a white cross and no emblem.
When was the Vatican City flag adopted?: The current design dates from 1929, and its official ratio is 1:1.

Vatican City Capital, area, population and currency
The flag of Switzerland Routinely mistaken for this one
Every flag with gold in it
The flag of Germany Ratio 3:5
The flag of Argentina Ratio 5:8
The flag of South Africa Ratio 2:3
The flag of Philippines Ratio 1:2
The flag of Chad Ratio 2:3
The flag of Jamaica Ratio 1:2
The flag of Ghana Ratio 2:3
The flag of Sri Lanka Ratio 1:2

Sources

Wikidata — Wikimedia Foundation (CC0 1.0)

How these figures are compiled and checked