A panel tackled board diversity at Fortune's Brainstorm Tech in Aspen, Colo.: Last spring the Wall Street Journal ran a story with a headline that perfectly summed up an issue most U.S. companies are struggling with: “Corporate boards are still mostly white, mostly male—and getting even older.” At Fortune's Brainstorm Tech in Aspen, Colo., on Wednesday, a panel of experienced board directors tackled the question of how to change the composition of corporate boards and why doing so is critical.