The flag of Libya (adopted on November 19, 1977) is plain green. It is the only national flag in the world with just one color and no design or insignia.
History
The first national flag of modern Libya was adopted when Libya gained independence from Italy in 1951. It consisted of a white crescent-and-star on a triband red-black-green design (with the central black band being twice the width of the outer bands).
Following the 1969 coup, the flag was replaced by a Pan-Arabic red-white-black triband. After the formation and dissolution of the Federation of Arab Republics (briefly linking Libya to Egypt and Syria), the current all-green design was adopted.
Symbolism
Green is the traditional colour of Islam, the state religion. It is also symbolic of Muammar al-Qaddafi's "Green Revolution".