At last, a reality television show about something important: no insect eating, no bad singing, no nubile bodies surviving suggestively, no Trumpery, no skating with no-account celebrities, for God’s sake. But just when you thought it was safe once again to turn on that telly, the folks at FX have gone and spoiled it all by taking a marvelous premise – a black and a white family exchange identities – and producing a middling stinker.

Not that there aren’t some compelling moments when the Wurgel family, of Santa Monica, Calif., meets the Sparks family, of Atlanta. Brian and Renee Sparks are black and angry about it; their 17-year-old son, Nick, can’t decide whether he’s Beavis or Butthead, but he’s happily along for the ride. The Wurgels are earnest in a California sort of way, full of therapy-speak about “growth” and “truth” and “mindfulness.” Carmen is pretty and makes a big point of introducing herself as being from a “very liberal” family; Bruno, who unaccountably has a different last name (Marcotulli), is a self-made believer in the power of positive thinking. Their 18-year-old daughter, Rose, would be happy on a surfboard or in an ashram as long as the experience felt “authentic.”

“Black.White,” which premieres tomorrow night at 10 p.m., does a pretty good job of establishing the individual personalities and preparing for the inevitable conflicts. Not only have the families agreed to “pass” as members of another race, they will also share the same house and coach each other on the fine points of racial difference.

Keith Vanderlaan, who gave Johnny Depp his epicene look for “Pirates of the Carribean,” should win an Emmy for his work on “Black.White.” Both families are convincingly transformed and able to function effectively in everyday situations. This becomes apparent in conversations about race with unsuspecting boobs like the longhaired habitue of a local bar who goes on and on about the alleged fecklessness of blacks while Renee seethes under her blond wig.

Predictably, though, the show quickly becomes a one-sided course in black culture for the Wurgels. The producers apparently endorse the Sparks’s periodic assertions that African-Americans know pretty much all they need to know about white people because they have had to adjust to the dominant culture.

Although this politically correct attitude is initially off-putting, it quickly becomes apparent that the Wurgels are, indeed, entirely clueless. What’s more, they are exceedingly annoying in an entirely uninteresting way and become the main reason the series’s disappoints.The Sparks become more and more sympathetic as the story develops; they are intelligent, if too sensitive, and ever so slightly damaged in an attractive way. Their completely hapless parenting skills, apparent from the start, will become a plot twist in the series and posit the question of whether their next “reality” destination ought to be “Nanny 911.”

Carmen and Bruno have problems of their own, mainly with each other. Carmen may be the more irritating of the two, but it’s close to a toss-up. One thing you can say in her favor is that she is an excellent illustration of a political liberal’s tone deafness on racial matters. At one point, she refers to a “beautiful black creature” and fails to understand why the Sparks take offense. Then she “outs” a marginally effeminate black teenager in front of his friends and wonders why this is such a big deal. Bruno functions often as a stereotype of the white guy who thinks that if all blacks adopted the right attitude, prejudice would be a thing of the past. While he makes some legitimate points – about the degradation of women in hip-hop music, about the social pathologies in too many minority communities – he does so in such a ham-handed way that he discredits his own ideas. Is this what the producers had in mind?