On Wednesday, police in the Indian city of Srinagar shot cannons loaded with purple water at Kashmiri Government workers who were protesting fuel price hikes. Here's an explanation for why police mark rioters with pretty colors:

To identify and arrest them later. Many water cannons on the market today come with a tank specially designed to store a semi-permanent colored dye. Once the water cannon is trained on a crowd, anyone hit by the spray will be easily recognizable by police.

Because shooting citizens with water cannons for exercising their constitutional rights is just a little too reminiscent of Civil Rights era police abuses, American cops do the next best thing: Use paintballs.

[T]he FN303—the "less-lethal" gun that caused the accidental death of an Emerson College student during World Series celebrations in 2004—can be armed with pellets that include paint instead of a more typical pepper spray-based projectile. Since last October, U.S. Border Patrol agents have used FN303s loaded with paint to police fences in Arizona and California.

Be on the lookout for funny colored SUV drivers if gas prices keep going up.

Senior Editor Brian Doherty on the pros and cons of civil disobedience.