Short answers, pulled from the story.
Light with a dominant wavelength between 570 and 590 nanometers creates the sensation of yellow for the human eye. This specific range places yellow directly between green and red on the visible spectrum.
Scientists like Grassmann and Helmholtz concluded that indigo or blue-violet wavelengths shorter than 450 nm served as the true complement. Modern CIE 1931 systems confirm that yellow around 580 nm pairs best with blue daylight white.
Yellow ochre pigment made from clay appeared in prehistoric cave art over 17,000 years ago. The Lascaux cave in France contains a horse image colored with this yellow pigment estimated at 17,300 years old.
Yellow lasers remain rare and expensive due to their complex generation requirements involving diode pumped solid state technology. Commercial products use infrared laser diodes to pump crystals containing neodymium-doped yttrium vanadium oxide or yttrium aluminum garnet to induce emission at exactly 593.5 nanometers.
During the Post-Classical period yellow became firmly established as the color associated with Judas Iscariot despite biblical silence regarding his clothing. This connection led to associations with envy jealousy and duplicity which later influenced Renaissance traditions marking non-Christian outsiders with yellow colors.