Green as the Only Primary Color

• In Color Standards and Color Nomenclature, by Robert Ridgway (1912), the author notes that "green [is], in fact, the only spectrum color that cannot be made by mixture of the other colors" (p 19). Apparently, it was believed that there were colors whose hues could not be reproduced by mixing other colors (additive primaries for additive mixing and subtractive primaries for subtractive mixing). Ridgway points out that this seems contrary to his own experience, as he was able to produce pure hues of red, and blue through additive mixing, but was unable to produce green in this way, so presumably then red and blue could not be primaries by the then-accepted definition. (This leads to the conclusion, not stated by him, that green is the only primary.) It should be noted that this is not just a crackpot book, as the author, curator of the United States National Museum's Division of Birds, appears to have been quite a careful observer, and A Dictionary of Color, mentioned below, describes this work and the author's preceeding edition as having been standards of color-naming for scientists for decades.
• In A Dictionary of Color, by A. Maerz and M. Rea Paul, 2nd ed (1950), the authors describe the case of Chineese Green, a dye that was brought over in the 1700s or 1800s (XXXcan't remember now, have to check). Apparently it was possible to produce any color of the spectrum with this dye merely by carefully varying the dying conditions.
• If one takes the spectral response curve of the human eye and uses it as a spectral intensity curve for a light source, that light will appear green, as noted about the CIE (1931) green additive primary Y in G. A. Agoston, Color Theory and Its Application in Art and Design, 2nd ed, 1987.