LOS ANGELES, California (CNN) -- There's no question "Tropic Thunder" takes chances.



Ben Stiller, left, and Robert Downey Jr. are among the stars of "Tropic Thunder," a Hollywood satire.



Tom Cruise almost unrecognizable as a foulmouthed, foul-mannered movie executive? Check. Mockery of action heroes, Method actors and gross-out comedians? Check. Challenging stereotypes at every opportunity? Absolutely.



But casting Robert Downey Jr. as a black man? Well, that might be a bit much.



Or maybe not.



In "Tropic Thunder," a comedy about self-absorbed Hollywood types making a "Platoon"-style war movie, Downey plays Australian actor Kirk Lazarus, a multiple Oscar-winning performer who gets so involved in his roles that he forgets to come out of them. He's a man constantly looking for ways to transform himself for his art.



So, cast as a black man in the war movie, Lazarus decides to dye his skin surgically.



Downey -- no slouch as an actor himself -- has often been seen as one who immerses himself fully in his roles. That kind of dedication prevented the character from coming off as offensive, said Ben Stiller, who directed, co-wrote and stars in "Tropic Thunder."



"I give all the credit to Robert," Stiller told CNN. "I felt he really was so committed to that character, the guy that was playing that guy, that as an audience you bought his sincerity. Very few people, I think, could pull that off."



Brandon Jackson, who plays hip-hop star turned actor Alpa Chino (say it fast), agreed.



"Robert was black the whole time. My mom came on the set and she thought it was Don Cheadle," he told CNN. "I'm serious. That's how black he was."  Watch Jackson talk about working with Downey »



The movie, which also stars Stiller as struggling action star Tugg Speedman and Jack Black as gross-out king Jeff Portnoy, features some testy altercations between Downey's Lazarus and Jackson's Chino. Lazarus gets so involved in his role that even when it's clear filming has wrapped for the day, he sticks with it -- which irritates Chino to no end.



"To me the most important thing was Alpa Chino has to give him a beat down and tell him that what he's doing is crazy the whole time," Downey said. "Otherwise it's just demeaning to Brandon's character. And if it's demeaning to an actual black man in the movie ... I would have run for the hills."



Jackson said he would have challenged the movie if the material was offensive. But, he said, "Tropic Thunder" is a long way from the days when white performers would don blackface as a way of exploiting black stereotypes. Since then, he said, the playing field has leveled: The Wayans brothers played "White Chicks" in the film of the same name, and Eddie Murphy has played several ethnicities in his films, including Jewish and Chinese characters.



"If we're all gonna play ball, let's all play ball," Jackson said. "I believe in fairness. If we can punch you, punch back. And funny is funny." iReport.com: Will you see 'Tropic Thunder'?



Stiller, of course, is no stranger to testing comedy limits. The actor, writer and director, known for films such as "Meet the Parents" and "Zoolander," has performed or created roles that strike a delicate balance between sympathetic and distasteful -- and sometimes fall too hard on one side of the line.



He co-wrote "Tropic Thunder" based on an idea he had in 1987, when many of his friends were making war movies, he recalls in the film's production notes. While Stiller was making "Empire of the Sun," his colleagues were in boot camps training for their military roles -- and would emerge talking about the boot camp as if they'd become part of a
what pushes boundaries at every opportunity?
"Tropic Thunder"
question: what pushes boundaries at every opportunity?, answer: "Tropic Thunder"