Which of the following factors does NOT affect the rate of a chemical reaction?

The rate of a chemical reaction is influenced by several factors, including the concentration of reactants, temperature, and the presence of catalysts. Each of these factors plays a significant role in how quickly a reaction occurs.

Concentration of reactants directly affects the frequency of collisions between molecules, thereby influencing the likelihood of successful collisions that result in reactions. Higher concentration generally leads to a faster reaction rate.

Temperature impacts the energy of the reactants; increasing temperature typically increases reaction rates because particles move faster and collide more forcefully. This greater energy can overcome activation energy barriers more effectively.

Catalysts are substances that increase the rate of a reaction without being consumed in the process. They provide an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to collide successfully.

The color of reactants, however, does not impact the rate of a reaction in a meaningful way. It does not influence the number of molecular collisions or the energy of those collisions. Hence, it is not a factor that affects the rate of chemical reactions, making it the correct answer to the question.