Short answers, pulled from the story.
Late Stone Age people began using red ochre at Pinnacle Point between 170,000 and 40,000 years ago. This activity involved scraping and grinding the clay to create a red pigment from iron oxide. The evidence was found inside cave 13B on the coast of South Africa.
The human eye sees red light when it looks at wavelengths between approximately 625 and 740 nanometers. This range defines the color red in the RGB color model. Light just past this range is called infrared and cannot be seen by human eyes.
Lasers emitting in the red region of the spectrum became available with the invention of the ruby laser in 1960. This invention enabled widespread scientific applications including holography and education. Red helium neon lasers were invented in 1962 and were used commercially in LaserDisc players.
Mars is called the Red Planet because its surface has a reddish color imparted by abundant iron oxide. This geological feature gives the planet its distinctive appearance. The iron oxide is present in the soil and rocks of the Martian surface.
The red military uniform was adopted by the English Parliament's New Model Army in 1645. This uniform was still worn as a dress uniform by the British Army until the outbreak of the First World War in August 1914. Ordinary soldiers wore red coats dyed with madder while officers wore scarlet coats dyed with cochineal.
The People's Republic of China adopted the red flag following the Chinese Communist Revolution. This event occurred after the Soviet Union adopted a red flag following the Bolshevik Revolution in 1917. The red flag was also adopted by North Vietnam in 1954 and by all of Vietnam in 1975.