If it makes you feel any better you didn't get spat at because you have red hair. Neither the color of your hair nor anything about you specifically had anything to do with the intentions of those boys. You got spat at because your accosters were looking to prank someone with little chance of retribution, which is why they sped off. They are cowards plain and simple and since they cannot rely on intelligence, bravery or self respect to feel good about themselves they are forced to random acts of dick waving to self-justify their existence. You should feel proud in fact that you touched a life today. Some boy who might have otherwise cried himself to sleep tonight or put a shotgun to his temple out of self loathing and utter life ineptitude can now look back on this instance and think (at least in his own mind) that he has importance. You sir are a potentially life saving hero and I applaud you for it!
For fairness of full disclosure I had a similar thing happen to me last winter. I was walking home in the snow at the side of a road when all of a sudden I felt a heavy slap on my back. At the same time I heard obnoxious laughter amid the tire squeal of a car that had swerved over sharply in order to throw a snowball at my back before speeding off. In reality I thought the prank was a little funny myself but I was angered that the car swerved into me on an icy road at speed. Had the driver not been able to control his car he could have killed me for such a prank. That is what pissed me off more than the snowball.
For fairness of full disclosure I had a similar thing happen to me last winter. I was walking home in the snow at the side of a road when all of a sudden I felt a heavy slap on my back. At the same time I heard obnoxious laughter amid the tire squeal of a car that had swerved over sharply in order to throw a snowball at my back before speeding off. In reality I thought the prank was a little funny myself but I was angered that the car swerved into me on an icy road at speed. Had the driver not been able to control his car he could have killed me for such a prank. That is what pissed me off more than the snowball.