Which factor does NOT affect a projectile's trajectory?

In the context of factors affecting a projectile's trajectory, color does not play a role. The trajectory of a projectile is influenced primarily by physical forces and properties, such as mass, air resistance, and initial velocity.

Mass affects how gravitational forces and air resistance impact the motion of the projectile; a heavier object will fall differently compared to a lighter one under the influence of gravity and air resistance. Air resistance is a critical factor, as it opposes the motion of the projectile, altering its path and speed as it travels through the air. Initial velocity determines the speed and angle at which the projectile is launched, directly influencing its range and height.

In contrast, color does not have any impact on these physical forces or the mechanics of motion, making it a non-factor in determining trajectory. This is why it stands out as the correct answer in this question concerning which factor does not affect a projectile's trajectory.