From Halopedia, the Halo wiki
Strange and inscrutable, the Hunter pair who identifies as "Colony" is believed to be either a representative for Lekgolo allied to the Banished or a specialized command form of the alien eel-worms. Colony defers only to Atriox and is charged with directing all Banished Lekgolo activities on the Ark, including creation and expansion of Lekgolo clusters for use in vehicles and other specialised applications. Though it cooperates with the Banished. Colony appears to have its own plans for the Ark. Most of its attention is currently focused on the activities near the resting place of the Forerunner keyships; missions undertaken outside the knowledge of other Banished leaders.
When called upon to direct Banished military operations. Colony's strategy is to control the battlefield with large numbers of Lekgolo-driven constructs that it can heal and augment, buying time with Engineer Swarm and Living Barriers until it can call in reinforcements with Colony Drop and Devastating Host. It can also enhance friendly vehicles by infiltrating them with gestalts, using Vehicle Symbiotes. But time is the main ally of Colony, as its Combat Repair passive ability slowly heals all friendly units and structures.