Color grading system for opals

[Calo]

Gemval.com is proud to announce the release of a Beta Version of the color grading system for natural opals. The system is used by Gemval as a basis for opal valuations. Please see how it looks here:
http://www.gemval.com/opal-color-grade.html

I'll highly appreciate your professional suggestions or any your intellectual contribution to Gemval's valuation methodology for precious opals - probably one of the most difficult gems for regular appraisal. I thank you in advance for your feedback!

Calo