Short answers, pulled from the story.
The sky appears blue because oxygen and nitrogen molecules scatter short-wavelength light toward our eyes. This optical effect is called Rayleigh scattering after Lord Rayleigh. Albert Einstein confirmed this phenomenon in 1911.
Prussian blue emerged in 1709 when Johann Jacob Diesbach discovered it while experimenting with dried blood and iron sulfides. By 1710 French painter Antoine Watteau used this new pigment. It became popular for wallpaper manufacturing and later for French impressionist painters.
Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura shared the Nobel Prize in Physics in 2014. Shuji Nakamura demonstrated high-brightness blue LEDs at Nichia Corporation in 1993. Isamu Akasaki and Hiroshi Amano worked on parallel developments at Nagoya University.
In the twelfth century, the Roman Catholic Church dictated that Italian painters dress Virgin Mary in blue to link the color to holiness, humility, and virtue. Pope Gregory I ordered all religious paintings to clearly tell stories to viewers. If Mary stood alone in an image, her costume used the finest blue pigment available.
Blue represents males beginning as a trend in the mid-nineteenth century. Gendered associations with blue became widespread from the 1950s onward. The color associated with males after World War II ended.