Quick, name a show about four tight-knit gal pals who aren't afraid to dish about sex! If you're thinking Sex and the City, think again. Girlfriends also follows a quartet of feisty females, while also tackling the complicated issue of race. As UPN kicks off Black History month, tonight's "Sister, Sistah" episode (airing at 9:30 pm/ET) explores what racially defines a person.

"It's a really huge topic they try to address in 22 minutes, and that's courageous," says Tracee Ellis Ross, who plays neurotic but loveable lawyer Joan. In the episode, Joan and Toni get upset when they meet Lynn's white sister, Tanya — who's gone a bit overboard in embracing black culture. Ross admits she caught some discrepancies in the original script and felt compelled to suggest changes to the show's producers.

"I'm of mixed race: My father is white and my mother is black," she explains. "The definition of blackness is something I have difficulty with. My character does say, 'What is acting black anyway?' That was my suggestion. I don't think that... the color of your skin defines who you are."

Now in its second season, the low-rated Girlfriends has had its ups and downs: It was recently nominated for an NAACP Image Award for outstanding comedy series — but it's also taken harsh criticism, most notably from filmmaker Spike Lee. Shrugs Ross: "Something I learned from my mom [singer Diana Ross] — and something you have to remember every day in this business — is don't believe the good things people say, and don't believe the bad. The biggest challenge for us is getting people to watch."