Which African country's flag was entirely green from 1977 to 2011? Libya. During that period, Libya used a plain green national flag with no emblem, stripe, text or other design.
The flag was adopted on 19 November 1977 under Muammar Gaddafi, following Libya's withdrawal from the Federation of Arab Republics. Its single color reflected Gaddafi's political philosophy, expressed in his Green Book, and was also associated with Islam and the country's agricultural identity.
For much of its existence, the plain green flag was exceptional worldwide. It was widely described as the only national flag consisting of one color and no design, although Afghanistan briefly used an all-white flag during part of 1996–1997. Libya's green flag remained in use until the 2011 uprising and fall of Gaddafi's government.
The current Libyan flag is different: it is a red, black and green horizontal triband with a white crescent and five-pointed star. That design was originally used by the Kingdom of Libya from 1951 to 1969 and was restored by the National Transitional Council in 2011.