Short answers, pulled from the story.
Grey is the dominant spelling in European and Commonwealth English, while gray is more common in American English. Both spellings are valid in both varieties. The distinction developed around the 20th century, though in HTML and CSS only gray is recognized, as this convention was inherited from the X11 color list.
The first recorded use of grey as a color name in the English language was in 700 CE. The word derives from the Old English grǣġ, related to the Dutch grauw and German grau.
The Confederate Army wore grey primarily because the South lacked a major dye industry and grey dyes were inexpensive and easy to manufacture. On the 6th of June, 1861, the Confederate government issued regulations designating cadet grey as the standard uniform color. The uniforms were designed by Nicola Marschall, a German-American artist.
Hair turns grey when melanocytes in the hair follicles reduce and eventually stop injecting melanin into growing hair cells. A team of Harvard scientists proposed in the February 2005 issue of Science that this decline results from the failure of melanocyte stem cells to maintain pigment production due to age or genetic factors. Generally, 50 percent of Caucasians are 50 percent grey by age 50.
Grey on televisions, computer displays, and telephones is created using the RGB color model. Red, green, and blue light combined at full intensity produce white; by lowering all three intensities equally, all shades of grey can be produced. In the RGB model, grey results whenever the red, green, and blue values are equal.
Grisaille is a technique in which a painting is first composed entirely in grey and white, then colors are added on top using thin transparent glazes. The grey underpainting provides the shading, visible through the color layers. When left uncovered, grisaille gives the appearance of carved stone. Rembrandt van Rijn and El Greco both used grey extensively in their work.