The Greens ÔÇö King Aegon II's party
The queen's faction at court, who crowned the king's eldest son the moment the king was cold.
The fuller tale
They take their name from a tourney gown. Alicent Hightower wore green to the great tourney at King's Landing while the princess wore Targaryen black, and the court chose sides by colour, which is a fair summary of how seriously either party took the constitutional question.
The greens held the capital, the crown's gold, the Hightowers and the Reach, and ÔÇö crucially ÔÇö the machinery of government, which meant that for the first year of the war they could pay soldiers while the blacks could only frighten them. Their case rested on the plain fact that Westeros had never crowned a queen and had already voted once, at the Great Council of 101, to say sons before daughters.
Aegon II won the throne, outlived his rival by months, and was poisoned by his own side. Nobody who fought this war got what they wanted, which is the entire lesson of the Dance and one the realm forgot inside a century.
The ground they held
What became of it ÔÇö if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.