© David Kaplan.
In both electrodynamics and the theory of the strong force, neutral objects, with a total charge of zero, tend to form due to the attraction of the charges. On the left, neutral atoms form because positive protons and negative electrons are attracted to each other and form bound states. On the right, the strong force can make two sorts of neutral objects: either a quark of some color, and an anti-quark of the opposing anti-color or three quarks, each of a different color. (Unit: 2)