Which of the following is NOT a factor that affects the voltage sustained by a hard hat?

The correct choice highlights that the color of a hard hat does not influence its electrical properties or the voltage it can sustain. Hard hats are designed primarily for safety and protection against impact and electrical hazards, and their voltage rating is determined by the materials and construction methods used, rather than their color.

Factors such as the cleanliness of the hat can significantly affect its ability to insulate against electrical current; contaminants like dirt and grease may create pathways for electricity, reducing the hard hat's effectiveness. The type of electrode contacted is important because different types of electrodes can conduct electricity differently, impacting how much voltage the hard hat can withstand. Additionally, weather conditions like humidity and temperature can influence the material properties of the hard hat, potentially affecting its insulation quality.

Thus, while cleanliness, electrode type, and weather conditions are vital to consider for maintaining the effectiveness of a hard hat in insulating against electrical voltage, the color of the hat has no impact on these critical factors, making it the correct choice for this question.