No surprise that Black in America, Soledad O'Brien's documentary series on African American life and culture, was among CNN's most-watched programs. No other show has offered a deeper look at what it means to be black, in all its complexities.

As provocative as the previous four broadcasts were, I dare say that nothing will cut to the core of black identity more than O'Brien's fifth installment, Who is Black in America?, at 8 p.m. Sunday on CNN.

If you know Philadelphia, you've got to tune in. The documentary is flush with Philly folks.

Students Nayo Jones and Rebecca Khalil of the Philadelphia Youth Poetry Movement explore racial identity, sometimes painfully, under the compassionate guidance of instructor Perry "Vision" DiVirgilio. Drexel professor Yaba Blay - whose (1)ne Drop project gave O'Brien the impetus for the documentary - shares her own story.

Along with O'Brien, all attended a packed screening this week at Drexel.

Like any good documentary, Who Is Black in America? left me pondering fundamental questions: Just who is black in America? Is blackness predicated on skin color or a cultural state of mind? And who gets to decide?

One little drop

Through the years, skin color has been politicized and racialized. Just look at President Obama. Even though he identifies as a black man of mixed race, his identity is the topic of endless public debate. As if he's going to change his answer.

After all, the "one-drop rule," a law adopted by some Southern states in the early 20th century, designated a person black if s/he possessed even a trace of black heritage - in effect, only one drop of black blood. By that rule, our biracial president would have had no chance to enjoy the privileges conferred on pure-lineage whites.

Today, multichoice census forms allow us to check off what we truly are. Yet colorism continues to shackle us in a racialized society.

Fortunately for O'Brien, her parents made it easy for her. Growing up in a white community on Long Island, María de la Soledad Teresa O'Brien, fair-skinned, freckle-faced, big-Afroed daughter of an Afro-Cuban mother and an Irish-Australian father, never had to grapple with the "What are you?" questions.

"My parents made it very clear: Do not let people tell you you're not black and not Latino," O'Brien, 46, told me. "They understood the hostility of the environment. ... You needed to be steeled."

The identity dilemma

Through photographs and personal stories of biracial subjects, Yaba Blay's (1)ne Drop project distills questions of racial identity into beautifully human narratives.

Blay, a professor of Africana studies, concedes she started (1)ne Drop to answer questions of her own.

After all, she is a seal-brown daughter of Ghanaian immigrants - not only a dark-skinned African American, but also a dark-skinned African. Research told her that people like her are almost always at an economic and social disadvantage simply because of that darker complexion.

Her share of social rejection embittered Blay with the belief that "lighter-skinned people lived these glorious lives." But with (1)ne Drop, Blay learned that multiracial people suffered a different brand of rejection.

"I've never had to defend my blackness," she says. "I can't imagine what it feels like to have people say my [identity] is not mine."

Fascinating stuff. Who Is Black in America? triumphs because it eagerly dives into uncomfortable truths that all too often get ignored.

"The only way to move forward," O'Brien says, "is to take these subjects out of the darkness and into the light."

So to speak.