A precise and shared description of gemstones color could greatly help their classification and market evaluation, and the key to develop an efficient color evaluation system for gemstones is the creation of a common descriptive language and assessment method. Nowadays, there is a lack of standards for the determination of color of gemstones, and traditional color assessment is exclusively based on the direct visual observation in some cases with lenses and microscopes. The underlying problem is that light impinging gemstones, due to their physical characteristics, produce scattering and multiple reflecting phenomena. This puts the process of gemstone color assessment out of the scope of classic colorimetry. What needs to be assessed is the overall appearance of the gemstone and this explain why, so far, it is realized mainly by visual inspection.