When I started my career at Fortune in 1984, corporate America was a land of white men. As I say in my talks about women and power, bosses back then were white men without facial hair.

We’ve come a long way—just look at Fortune’s Most Powerful Women list.

But a new report on Fortune 500 board composition, released by the Alliance for Board Diversity this morning, should make diversity champions weep.

The boards of America’s biggest corporations are getting whiter. At the top 100 companies on the Fortune 500, African-Americans held 4.2% of the total board seats in 2010. That’s down from 7.8% in 2004.

In the six years that passed, African-American men lost 42 board seats. White men gained 32.

The trend defies calls for independent boards and goes against evidence that diverse boards deliver superior returns to shareholders.

As for women on boards, the study indicates scant progress. Women fill only 15.7% of directorships in the Fortune 500.

And in the upper tier of the Fortune 500, which companies have the broadest board diversity in terms of gender as well as race? Citigroup , IBM , and Procter & Gamble .

We’ll learn more on the topic today when my colleague, Fortune Executive Editor Stephanie Mehta, leads a discussion with Heidrick & Struggles Vice Chairman Bonnie Gwin. This session will lead in to tonight’s Most Powerful Women dinner in Washington, D.C.. This evening, Fortune Washington Editor Nina Easton interviews Fran Townsend, who was one of President Bush’s top advisors on national security. Timely stuff, all around. Come back to Postcards tomorrow for the lowdown.