Short answers, pulled from the story.
Green is evoked by light with a dominant wavelength of roughly 495 to 570 nanometers, sitting between cyan and yellow on the visible spectrum. The dark-adapted human eye is most sensitive at about 507 nanometers, while the light-adapted eye peaks near 555 nanometers.
Plants are green because of chlorophyll, the chemical involved in photosynthesis that absorbs red and blue light efficiently but green light poorly, so the light plants reflect is enriched in green. Chlorophyll absorbs green poorly because it arose in oceans where purple halobacteria were already using the green part of the spectrum.
Green is the traditional color of Islam because, according to tradition, the robe and banner of Muhammad were green, and the Koran says those in paradise wear green silk robes. It was adopted as a Shi'a color and appears in the flags of nearly all Islamic countries.
The reverse side of the US dollar bill has been green since 1861. Green was originally chosen because it deterred counterfeiters using early camera equipment and because the thin banknotes did not let the green show through to the front.
In languages including old Chinese, Thai, old Japanese, and Vietnamese, a single word can mean either blue or green. Green appears as a separate color category only in languages that have developed a full range of six basic colors, or more rarely five.
In post-classical and early modern Europe, green was worn by merchants, bankers, and the gentry, while red was reserved for the nobility. The Mona Lisa wears green, and the British House of Commons benches, where the landed gentry sat, are green, while the House of Lords benches are red.