Paintball is a game where markers or guns are filled with non-lethal paint put in gel-like capsules which basically are used to shoot opponents. These markers are propelled by compressed gas.
Markers used in paintball evolved through the years - their use now is not the reason they were created years ago.
Markers for trails, trees and cows:
Believe it or not, the use of these markers started in the 70's when farmers and members of forest groups used them to mark trees as well as trails, and cattle. The guns used then were powered by gas. Then - whether by inspiration or boredom