Here's where by a supplier would include Form 2 coloured gemstones, assuming the supplier is appropriately identifying the gemstones and classing them in the proper grade. Some gemstones have lots of colours. As in the case of tourmaline and ametrine, this may possibly seem as colour zoning. In other cases, https://www.gemsbiz.com/blog/explore/a-guide-on-diamond-quality-grading-parameters