What do the colours of the Serbia flag mean?

Red: pan-Slavic; the top band. Blue: pan-Slavic; the middle band. White: pan-Slavic; the bottom band.

How do you tell the Serbia flag from the Russia one?

Russia is white-blue-red; Serbia is red-blue-white — the same bands reversed.

When was the Serbia flag adopted?

The current design dates from 2010, and its official ratio is 2:3.

The flag of Serbia

Three equal horizontal bands of red, blue and white, with a coat of arms — a crowned double-headed eagle — set toward the hoist.

Ratio 2:3 · current design adopted 2010

Serbia's tricolour is Russia's upside down, a deliberate nineteenth-century nod: the Serbs took the pan-Slavic colours and inverted the order. The civil flag has no arms; the state flag does, and the two are used in different contexts by law. The 2010 revision moved the arms slightly and adjusted the shades after the 2004 restoration of the monarchy-era design. The four firesteels around the cross are widely explained as the letters of "Only unity saves the Serbs", a reading that is traditional rather than documented.

Flags it gets confused with

Flag	How to tell them apart
Russia	Russia is white-blue-red; Serbia is red-blue-white — the same bands reversed.
Slovakia	Slovakia is white on top with a double cross, not an eagle.

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
Double-headed eagle	The Nemanjić dynasty, and Byzantine inheritance
Cross with four firesteels	The Serbian cross; the four shapes are commonly read as the initials of a Byzantine motto

Ratio: 2:3
Current design adopted: 2010
Colours: red, blue, white

Common questions

What does the flag of Serbia look like?: Three equal horizontal bands of red, blue and white, with a coat of arms — a crowned double-headed eagle — set toward the hoist.
What do the colours of the Serbia flag mean?: Red: pan-Slavic; the top band. Blue: pan-Slavic; the middle band. White: pan-Slavic; the bottom band.
How do you tell the Serbia flag from the Russia one?: Russia is white-blue-red; Serbia is red-blue-white — the same bands reversed.
When was the Serbia flag adopted?: The current design dates from 2010, and its official ratio is 2:3.

Serbia Capital, area, population and currency
The flag of Russia Routinely mistaken for this one
The flag of Slovakia 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 Italy Ratio 2:3
The flag of Mexico Ratio 4:7

Sources

Wikidata — Wikimedia Foundation (CC0 1.0)

How these figures are compiled and checked