By now it was understood that two quarks can form a meson, and three can form protons, neutrons, and other handrons. A theory was advanced in which there are three types of quarks dubbed red, blue, and green. Like light, a red, blue, and green quark will combine to give a lack of color (white), and only combinations yielding white can exist.
A visual chronology of Asimov's ~1500 scientific inventions and discoveries.
