There were three distinct styles of shoes used. Clown shoes are usually found in red but rarely seen in black - perhaps the black shoes were used to deplete excess inventory.
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Turned up toes

The very earliest clowns wore heavy looking shoes with a turned up toe area.

Turned down toes

Later, the shoes were tapered so that the toes areas were down turned.

Straight toes

The last distinct shoe style modified the second style to turn the toe area up again so that they are about straight.