Why is Libya's flag just green?

First, we should note that the all-green flag has been retired since the fall of Gadhafi and replaced with the Senussi Standard, which flew over Tripoli during the reign of King Idris I of Libya (chief of the Senussi Muslim Order).

However, the reasons that Gadhafi chose to make the flag green are several. Green is the traditional color of Islam and represents growth and flourishing, given the rarity of seeing green in a desert-country like Libya. The color also represents Gadhafi's the Green Book, a 1975 collection of Gadhafi's personal views on everything from science to history and which rarely features facts of any substance. The Green Book was required instruction in Libya while Gadhafi was in power.