These are very special stones, the color is native to the material* and not a coating. There is a very limited supply of these colors!
Click on the link below for info. Subject to availability.
https://docs.google.com/a/schubach.com/spreadsheet/pub?key=0AiffSP2ibG2qdFhScGp2eGQ5eE5FQ3hweHc4M1pxZ2c&output=html
*Except for the purple stones which are coated