Ever since I first saw him in AMC’s “Fear the Walking Dead” in 2015, Colman Domingo has impressed the hell out of me as an actor, and made me want to watch everything he was in, even when the material failed to live up to his outstanding talent.

So I was already sold on seeing his starring role in Clint Bentley and Greg Kwedar’s “Sing Sing.” What made it even better was that the rest of the movie, including his co-stars, more than matched the superb performance I’ve come to expect from him.

This is especially notable because “Sing Sing” is based on the real-life Rehabilitation Through the Arts (RTA) program at the Sing Sing Maximum Security Prison in New York, and Domingo’s co-stars are, almost without exception, the actual prison inmates who took part in the program, playing themselves.

Normally, playing yourself tends to be regarded as lazy acting. What makes it remarkable in “Sing Sing,” however, is that these men came from backgrounds that were aggressively, even violently, hostile toward men expressing themselves emotionally.

So after these men did the hard work of breaking down their own emotional boundaries, as all effective actors learn to do, they volunteered to rigorously and honestly examine themselves as they once were, to play the people they used to be, flaws and all.

This can be a Herculean undertaking even for folks who aren’t saddled with lifetimes of toxic masculinity. I was particularly struck by the moving performances of Sean “Dino” Johnson, whose heartfelt plea for empathy befits a man who’s made a real-life career out of conflict mediation, and Clarence “Divine Eye” Maclin, who essentially serves as a co-lead actor to Domingo in this film.

Maclin had to get over his reflexively confrontational machismo in order to work within the collaborative partnership of the RTA cast. On top of that, he had to expose his former mindset and behavior by acting it out, with occasionally unflattering authenticity.

What’s wonderful about this movie is how much it embraces play and vulnerability as sources of healing, not just for acting out serious dramas by Shakespeare but also in goofing around in intentionally silly comedy skits, as we see the RTA cast presenting here.

For men whose childhoods were often tempered by too-harsh adult realities, there’s something beautiful about seeing a bunch of hardened tough guys throw themselves into playground-style slow-motion sword-fights with cheap prop weapons.

“Sing Sing” also acknowledges that getting in touch with the emotional core of a character that you’re playing requires you to know and make peace with who you are, and that can be scary.

Early on, Maclin struggles  to submit to the process, by being willing to make mistakes and lay himself bare before others. Similarly, Domingo shows how John “Divine G” Whitfield, who busies himself with the RTA program and helping fellow inmates obtain parole, eventually breaks from the strain.

Domingo portrays Whitfield, whose bid to play Hamlet loses out to Maclin’s audition, as being not unlike Shakespeare’s Prince of Denmark. Like Hamlet, Domingo’s Whitfield is bounded in a nutshell, incarcerated for a crime he didn’t commit, but he counts himself a king of infinite space by making the RTA productions his entire remaining world.

Even before his eventual outburst in front of his peers, in frustration from working so long to obtain his release from prison, Domingo delivers a master class in how to play the granular erosion of stoic fortitude, in the face of sustained everyday hardships.

One sequence in which “Sing Sing” gets downright metafictional is a late-night conversation between Domingo and Sean San José. As neighboring cellmates, talking through the wall between them, they wax nostalgic about their younger years.

Because both men are sitting with their backs to opposite sides of the same wall, they look over their shoulders to talk in each other’s direction. That leads to several moments in which each actor stares directly into the camera as he holds forth, with an almost Kubrickian intensity.

Oddly enough, it reminded me of after-dark conversations I had with fellow service members when I was in the military, when we were both so tired, and had been through enough together, that we could no longer put up emotional walls between us.

“Sing Sing” is such a humane film. Please see it.