Well, yes, there is a gemset, but it’s been out of production for several years and never reallly caught on. There is also Gemdialog, but that isn’t in wide use, either. I have the Gemworld Guide’s World of color, which consists of a book of graded Munsel type colors of various hues, saturations and tones. These all give numerical ratings to hue, saturation and tone, so technically I am wrong, there are color ratings which are rather exact. However, and this is what I was getting at, you won’t find any of these in common use among sellers and they are still dependent on the skill of the evaluator and are somewhat subjective. If you’re selling, you can/should describe the color with the GIA color names (e.g., strongly greenish blue, etc.) as best you can and use photos, altho’ you will find that some colors are notoriously difficult to photograph correctly and it seems that the camera will often impart an off color to the white background you should be using. Your best bet is to describe honestly as best you can, use good photos and offer a return privilege.