Which of the following factors is NOT directly influenced by gear tooth design?

The selection of "gear rotation color" as the factor that is not directly influenced by gear tooth design is accurate because gear tooth design primarily affects the mechanical performance characteristics of gears. Load capacity, noise levels, and operating speed are all parameters that can be significantly influenced by the shape, size, and configuration of the gear teeth.

Load capacity is impacted by the surface area and contact geometry of the teeth, which determines how much load they can bear before failing. Noise levels are affected by how smoothly the gear teeth engage and disengage, which is a direct result of tooth profile and spacing; poorly designed teeth can lead to increased vibration and noise during operation. Operating speed is influenced by the pitch and design of the teeth, as this can dictate the efficiency of power transfer and the potential for issues like slippage or wear at high speeds.

In contrast, gear rotation color is not a functional aspect of gear performance and typically depends on external factors such as the material or finish of the gear, rather than the tooth design itself. The focus of gear tooth design is primarily on enhancing performance in terms of mechanical interactions, rather than aesthetics or color.