Flag colours can represent almost anything: courage, nature, religion, sacrifice, peace, the land, a political movement or a country's history.
Red
Red is often associated with courage, sacrifice, struggle or blood, although its meaning varies widely. It is one of the most common colours on national flags.
White
White is frequently linked with peace, purity or honesty. In other contexts it may simply be part of a historic colour combination.
Blue
Blue can represent the sea, sky, freedom, loyalty or national heritage. It is especially common on flags of countries with strong maritime traditions.
Green
Green is often associated with land, agriculture, forests or Islam, depending on the country and its history.
Yellow and gold
Yellow or gold can represent wealth, the sun, prosperity or natural resources. In some flags it is mainly used for visual contrast.
There is no universal flag colour dictionary
The important point is that colour meanings are not universal. The same red, green or blue can have a completely different explanation from one national flag to another.