First sentence: "Color is a spectrum: Red fades from orange to yellow, whereas green merges to turquoise, then blue." Not true… Or where is brown on this spectrum?
Browns are dark oranges. The only color you won't find in the spectrum is purple, which is the combination of red and violet. Take a look at the "CIE color diagram", all the colors on the perimeter of the curved line are single wavelength colors. The straight line at the bottom requires a combination.