Cambridge, Mass.

LAST week, the Senate majority leader, Harry Reid, found himself in trouble for once suggesting that Barack Obama had a political edge over other African-American candidates because he was “light-skinned” and had “no Negro dialect, unless he wanted to have one.” Mr. Reid was not expressing sadness but a gleeful opportunism that Americans were still judging one another by the color of their skin, rather than  as the Rev. Dr. Martin Luther King Jr., whose legacy we commemorated on Monday, dreamed  by the content of their character.

The Senate leader’s choice of words was flawed, but positing that black candidates who look “less black” have a leg up is hardly more controversial than saying wealthy people have an advantage in elections. Dozens of research studies have shown that skin tone and other racial features play powerful roles in who gets ahead and who does not. These factors regularly determine who gets hired, who gets convicted and who gets elected.

Consider: Lighter-skinned Latinos in the United States make $5,000 more on average than darker-skinned Latinos. The education test-score gap between light-skinned and dark-skinned African-Americans is nearly as large as the gap between whites and blacks.

The Harvard neuroscientist Allen Counter has found that in Arizona, California and Texas, hundreds of Mexican-American women have suffered mercury poisoning as a result of the use of skin-whitening creams. In India, where I was born, a best-selling line of women’s cosmetics called Fair and Lovely has recently been supplemented by a product aimed at men called Fair and Handsome.