For more information on standard treatments for colored gemstones, we recommend visiting two important websites in the gemstone industry. Go to the American Gem Trade Association or the Gemological Institute of America's (GIA) website. At the GIA website you can read a guide on how to purchase a gemstone - a GIA Colored Stone Tutorial. For specific information about each stones routine enhancements, click at the bottom of the page on "Gem Library". Then go to a specific type of stone and click on "routine enhancements".
If you are considering purchasing a gemstone from a source that implies or specifically tells you that their gemstone is not enhanced (and this is a gemstone that is routinely enhanced) request to see an identification report for that specific gemstone. If one is not provided, ask that the specific gemstone you wish to purchase be sent to a reputable gem lab for an identification report. (Of course, this may not be reasonable if the stone is inexpensive but if it is an exepnsive stone you may one to request one.) Then when you decide to purchase the stone you will be buying with confidence and feel like you have made an informed purchase.