The Apple Pro Mouse was introduced in 2000 along with the G4 Cube. This mouse dropped the rubber ball used for tracking in all previous Apple mouse designs and replaced it with a solid-state LED optical sensor. The design of the mouse appeared to feature no buttons, but the entire mouse surface allowed for a single click. The shape of the mouse was an an elongated rectangle with two round sides (replacing the previous round design).
The surface of this mouse was crystal clear acrylic with a base insert in black that matched the keyboard that shipped with it. The original translucent gray/silver cable was less rugged than the mouse with a white cable that replaced it in 2003. Both examples are shown below.
The Apple Pro Mouse also included a ring to allow for three different click force settings on the underside of the mouse.