There are a number of concepts in model theory - often situated around Hrushovski's amalgamation method (see for instance http://math.univ-lyon1.fr/~wagner/nijmegen.pdf) - which are colorfully named:
Green fields (e.g. http://arxiv.org/pdf/1003.5149.pdf)
Red fields, or red additive groups of fields (e.g., http://projecteuclid.org/download/pdf_1/euclid.jsl/1174668392)
Green, white, black, and emerald points (e.g., http://arxiv.org/pdf/1401.0495.pdf)
My question is, where does this terminology come from? And is there a pattern to it - that is, would it have been as reasonable to call black points "white points" instead, or would that violate some broad convention?
