“You can call me anything in the book when I was younger. Just don’t call me African,” Jason Reynolds told me. That, he said, was “the worst insult a dark-skinned boy, as a child, ever got.” “Africa,” he explained, “is still equated to savage.”

Reynolds, a student at the University of Maryland, was not talking about racist remarks by white people. In fact, many white people don’t have a clue that “colorism,” the kind of prejudice Reynolds was talking about, even exists. Among black Americans, however, it’s an open secret.

“I’ve benefited from the colorism, because I’m light-skinned, because I’ve always had the long, straight hair,” said another black UM student, Marquita Briscoe. “I thought I was just pretty.” In music videos, it often turns out, both light- and dark-skinned African-American women can be sexy – just not in the same way. “The darker the woman is,” said Karen Morrison, also of UM, “she takes on what I refer to as … a ‘ho’ complex. She is the prostitute.”

“The lighter a woman is, well, she’s the goddess,” said Morrison, who is dark. “She’s the untouchable. She is the woman that all the men in the video aspire to have.”

Apparently, a shade close to white is useful if you want to play a successful character in the movies. Mel Jackson, who played a business executive in “Soul Food,” says light skinned men like him tend to get those white-collar roles. “If the character’s supposed to be more successful or more, more articulate or have a better background, they’ll easily cast me in that character.”

The Black Power movement was supposed to change colorist attitudes, and it did change some things in Hollywood. Dark-skinned male stars like Richard Roundtree began to get roles as action heroes. And now there are plenty of dark-skinned stars, such as Oscar winners Denzel Washington, Jamie Foxx, and Morgan Freeman.

Washington, Foxx, and Freeman, however, are men. If a black actress is to become a leading lady, she’d better be light, or maybe Hispanic. Wendy Raquel Robinson plays upscale roles. “I do have some peers that are a lot darker than myself,” she says. “They don’t get the opportunities.”

Is colorism universal among black Americans? That’s like asking whether racism is universal among white (or black, or Asian, or Hispanic) Americans. Some are openly prejudiced. Others may feel no bias at all.

But research suggests that colorism is in fact prevalent in real life, among both black and white Americans. In an experiment supervised by Connecticut College social psychologist Jason Nier, test subjects were asked to look at photos of faces, and then rate how smart they thought the people in the photographs were. Mixed in with the 60 photos were pictures of the same person, altered to look darker. In that and similar tests, the lighter skinned people were perceived to be smarter and wealthier, even happier. Both whites and blacks often gave lower scores to people with darker skin.

Historians say the friction among some blacks of different shades began during slavery, because light-skinned blacks, often the children of slaves and their white masters, got better treatment. “They were the ones who maybe worked in the house,” says historian Anthony Browder, “as opposed to the darker skinned Africans who worked in the fields, who were beaten more readily.”

Author Marita Golden says the association of light skin with privilege continued after slavery, preserved by the lighter black Americans themselves. They formed “blue vein” societies, organizations just for people whose blue veins could be seen through their skin. And to get into some churches, fraternities and nightclubs, you might have to pass the “paper bag test.” “The paper bag would be held against your skin,” Golden explains. “And if you were darker than the paper bag, you weren’t admitted.”

In Spike Lee’s movie “School Daze,” characters called one another such names as “high yellow heifer,” “tar baby” and even “wannabe white.” Lee was criticized by some blacks for being too honest about colorism. But this is a problem America has to face. It subverts the goal of a society in which we are judged only on individual merit. Colorism cannot be fought, even in our own minds, if we do not identify it.

It’s one more thing to think about when we talk about a color-blind society.

Mr. Stossel is co-anchor of ABC News’ “20/20.” ©2005 by JFS Productions Inc.