Just as the process of learning is a path to travel for us, so too is the process of discovering previously unknown areas of the language. One of these areas appears to be with colours. In TKD we are given the basic terms, there are two words that describe the colour range from red, through yellow and green, to blue. The boundary appears somewhere in the middle. Granted this is partially inferred as the colours specified in the dictionary definitions are not necessarily in the same order. This very basic sketch was expanded upon in KGT, allowing the more precise description of a colour, if necessary. It could be a cultural artefact that going in to such detail to differentiate colours is not deemed necessary or is deemed overly pedantic. This knowledge on describing colour may be expanded upon further at a later date. Be aware, for our own species, colour perception appears to be very dependent on language itself there is research on how various colours are differentiated by the languages of the world which you might find interesting as ancient Greek is one of them. https://en.wikipedia.org/wiki/Blue%E2%80%93green_distinction_in_language http://www.laphamsquarterly.org/sea/winelike-sea http://www.radiolab.org/story/211119-colors/