In the '80s, it was hard to imagine Sean Penn as anyone but the stoned surfer Jeff Spicoli from Fast Times at Ridgemont High. But in 1988, he surprised us all by playing a fast-tempered cop fighting gang members in the movie Colors.Released April 15 of that year, Colors is now celebrating a quiet 30th anniversary. I guess it's hard to celebrate a milestone for a movie that showed much of America a crime problem nobody wanted to see."Almost without exception, American movies about gangs have either romanticized them in fantasies or viewed them from outside as a monolithic, dangerous unit," the critic Roger Ebert wrote in his review. "This movie tries to understand a little of the tragic gang dynamics, to explain why in some devastated inner-city neighborhoods they seem to offer the only way for young men to find power and status."The movie starred Penn and Robert Duvall as two cops – one young, the other a street-tested veteran – assigned to the LAPD's new gang unit. It was indeed a "special movie," as Ebert described it – not simply a buddy-buddy cop movie but a thoughtful dive into gang culture and the helplessness of the forces assigned to corral it.Here are three things you probably didn't know about Colors on its 30th anniversary.1. Real gang members were used as security on the set and as actors. (Two were reportedly shot during production.)2. Penn himself did some time in 1987 – 33 days in jail – for hitting an extra on the set who was taking pics of the actor without his permission.3. The original script for Colors had the movie set in Chicago and was focused more on drug dealing. Director Dennis Hopper ordered a rewrite to place the story in gang-riddled Los Angeles.