"Black and White" is a vintage Three Dog Night hit that still pops up on oldies radio: "A child is black/A child is white/The whole world looks upon the sight."

But what does it see, really? "A beautiful sight," as the '70s ditty concludes? Or differences that, like it or not, still matter? FX offers a searing new reality check in its real-life saga "Black. White." Perception is the point, whether it's my race or yours, or how each of us defines ourselves.

This six-week series gets under the skin - literally and emotionally - through walk-a-mile-in-my-shoes disguise and live- together intimacy. One family of each race has moved into a Southern California two-story where they'll undergo a grueling makeup routine to go out into the world wearing a persuasive face of another color. Bruno and Carmen Wurgel and her college daughter Rose will get a taste of being perceived as black. Brian and Renee Sparks and teen son Nick will see where whiteface can take them.

These "progressive" people think they've got the racial equation down cold. They don't. And neither, as viewers tellingly learn, do we. "Black. White." serves to detonate an avalanche of soul- searching and conversation, in our lives as much as theirs.

Its dress-up switch may sound almost like playtime. But this being FX - home of such provocative dramas as "The Shield," "Nip/ Tuck" and "Rescue Me" - the result proves uncompromisingly revelatory. Documentarian R.J. Cutler ("American High") and producing partners Ice Cube and Matt Alvarez have chosen participants of strong personalities and fiercely held convictions. Yes, it's fascinating to see their physical transformations and how they're treated on their forays into shops and cafes with their new "reverse" identities. But the most illuminating drama comes back in that house, when they respond not just to any "truths" they've uncovered, but to each other's expectations and certainties.

Cutler's fly-on-the-wall filming is so raw, your gut churns with reactions to these fiery folks. Bruno, the show's most assertive (if not cocky) personality, admires the "superior" physical skills of blacks. He starts practicing a "black" walk, and hoping the worst racial epithet will come his way so he can test his "theory" that black reactions contribute to the word's power. More wide-eyed and proudly liberal, Carmen wants to experience the "secret society" of another race. The white couple's eager-beaver, let's-play-black attitudes put the more sensitized Brian and Renee sharply on the defensive. And that brews a stew of misunderstood motives and tearfully misconstrued statements.

Rose, clearly the show's most receptive soul, rolls her eyes at her parents' anxious efforts, confessing to the camera her fear of "falling into stereotype." She's excited but nervous about joining a black poetry-slam group, saying, "I don't want to be just sending out bull--." Nick won't send out anything. Uninterested, he goes through the motions at a Beverly Hills etiquette class. He thinks his world is color blind - even as the N word makes its generationally inevitable appearance. "Right" and "wrong" are less significant than the presumptions exhibited by this volatile mix of six, with their array of life experiences and attitudes. The show's makers put that together as a disparate team themselves: Cutler, the white and redhaired documentarian from Great Neck, and Cube, the black L.A. rapper- producer "straight outta Compton."

"The principal thing we were looking for," Cutler said in a phone interview, "was people who self-identified as open-minded, open- hearted and experienced with diversity - people who believed that a diverse society is a healthy society. We didn't want to look at self- proclaimed racists. We wanted to look at self-identified progressives. Because race in this country really isn't a matter of left or right. It's something much deeper."

Indeed, overt prejudice isn't what sets up the show's most explosive moments. It's Carmen attempting to compliment a member of Rose's poetry group with a vivid turn of phrase that strikes her listeners as betraying an air of racial superiority. It's Bruno resisting again when yet another black person explains he doesn't "get it" when it comes to the subtleties of bias. It's the "black" Wurgels exploring an unfamiliar culture, while the Sparks family already operates in the dominant world every day.

It's seeing social theories put into personal action. Bruno's in- your-face attitude makes him a lightning rod that Cutler finds telling. "I would suggest that an awful lot of white people in America, on all sides of the political spectrum - if you took his points of view, uninflected, and listed them, and put 'agree or disagree,' an awful lot of people would check 'agree' from top to bottom."

Judging the behavior in "Black. White." is thus not so simple. These "broad-minded" people are our surrogates, and this is our experience, in spirit if not in detail. Watching can be discomfiting, yet invigorating. "One of the conclusions of the show is that these things must be talked about," Cutler says. "And it's OK. We'll be OK if we talk about them." He sure knows how to start a conversation.

BLACK. WHITE. Remarkable makeup allows two families to "switch" races while sharing a house in which reactions quickly become explosive. Six-week docu- series premieres tonight at 10 on FX.