Colin, played by Callum Howells, is the quietest of the group and struggles to explore his sexuality throughout the show. In an interview with Esquire, Howells said that, for him, Colin's character explored innocence and his naivety. In the first episode, Colin starts working at a men's tailoring shop on Savile Row, where his boss tries to coerce him into sexual acts.
Later in the episode, we see Colin living with a friend of the family — a friend whose son gives him his first sexual experience. It's this pivotal scene that leads to Colin's downfall in later episodes, as his epileptic seizures are brought on by an HIV diagnosis, which later turns into AIDS. After a while in the hospital, Colin passes away in the third episode.
Image Source: Channel 4