Final answer:
Colin Powell most clearly represented the diversity of the U.S. to other countries through his role as Secretary of State, making him a key figure in U.S. diplomacy and international relations.
Step-by-step explanation:
The appointee from the choices provided who most clearly represented the diversity of the U.S. to other countries is Colin Powell. As a figure with a military background and a statesman, Powell served as the Secretary of State under President George W. Bush. His role as Secretary of State was of considerable global significance, with Powell being the first African American to hold this position. He was at the forefront of U.S. diplomacy and represented American interests and diversity on the world stage.
Other individuals listed, such as Clarence Thomas, had significant careers with notable appointments, such as Thomas' controversial confirmation to the Supreme Court. However, these roles were more domestically focused, and thus did not have the same level of direct representation abroad as Colin Powell's role as Secretary of State.