What do the colours of the Guatemala flag mean?

Sky blue: the Pacific and the Caribbean, which the country lies between. White: purity and peace.

How do you tell the Guatemala flag from the El Salvador, Honduras and Nicaragua one?

All three keep the bands horizontal; only Guatemala turned them vertical.

When was the Guatemala flag adopted?

The current design dates from 1871, and its official ratio is 5:8.

The flag of Guatemala

Three equal vertical bands of sky blue, white and sky blue, with the coat of arms — a quetzal, a scroll, crossed rifles and swords in a laurel wreath — on the white.

Ratio 5:8 · current design adopted 1871

Guatemala, El Salvador, Honduras and Nicaragua all fly blue-white-blue derived from the flag of the United Provinces of Central America, which dissolved in 1841 — the family resemblance is a shared constitutional history, not imitation. Guatemala is the one that turned the bands vertical, in 1871, which makes it the easiest of the four to identify. The quetzal is also the name of the currency. The rifles are Remingtons, drawn accurately enough to date them.

Flags it gets confused with

Flag	How to tell them apart
El Salvador, Honduras and Nicaragua	All three keep the bands horizontal; only Guatemala turned them vertical.
Argentina	Argentina's bands are horizontal with a sun, not a quetzal.

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
Resplendent quetzal	Liberty; the bird was believed to die in captivity
Scroll	The date of Central American independence, 15 September 1821
Crossed rifles and swords	Willingness to defend that independence by force if needed

Ratio: 5:8
Current design adopted: 1871
Colours: sky blue, white

Common questions

What does the flag of Guatemala look like?: Three equal vertical bands of sky blue, white and sky blue, with the coat of arms — a quetzal, a scroll, crossed rifles and swords in a laurel wreath — on the white.
What do the colours of the Guatemala flag mean?: Sky blue: the Pacific and the Caribbean, which the country lies between. White: purity and peace.
How do you tell the Guatemala flag from the El Salvador, Honduras and Nicaragua one?: All three keep the bands horizontal; only Guatemala turned them vertical.
When was the Guatemala flag adopted?: The current design dates from 1871, and its official ratio is 5:8.

Guatemala Capital, area, population and currency
The flag of Argentina Routinely mistaken for this one
Every flag with sky blue in it

Sources

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

How these figures are compiled and checked