Hillary Clinton and Leon Panetta participated in a formal "conversation" at National Defense University. Secretary Clinton wore a signature monochrome pantsuit and white pumps:
You've probably heard the "rule" before about no white after Labor Day (or before Memorial Day), and this rule is most commonly applied to shoes and bags specifically. Whether you adhere to this rule or you don't, there's more to consider when choosing a white shoe than just the calendar. A white shoe or bag will "pop" or stand out significantly more when it's close to another, colored item of clothing. In this case, her pants come very close and touch her shoes (obviously) which makes the white color stand out. They also stand out as the only non-blue part of her outfit, on a stage where she is visible from head to toe.
My advice in this case would probably not be to draw the eye down to the shoes in this way, so I would recommend a beige shoe instead. It's still light and summery, but would blend more seamlessly in to the rest of the look.