Second driver of quality is the clarity. This is all about inclusions in the gemstone. Almost all natural gemstones have inclusions. Collectors search for gems with the least amount of inclusions, these are the most valued. However, sometimes a unique inclusions become the value factor e.g. horsetail inclusion.
Diamond clarity is well standardized. This standard can not applied for colored gemstones – if so, all colored gems would all be of poor clarity. To complicate matters, there is no international standard for gemstone clarity. As a result, gemstone clarity is graded in many ways.
Note that colored gemstone clarity is judged in terms of how clean it appears on naked eye, not on loop.