With regard to color, a color grade of G is a Near Colorless stone. Therefore, it should not appear “milky white.” Here’s our brief primer on diamond color: http://4cs.gia.edu/EN-US/diamond-color.htm

There is a color called “fancy white,” and although white is not a spectral color, it is considered a colored diamond. The white is caused by submicroscopic inclusions, and in these rare cases, tiny inclusions can produce a translucent milky “white” color by scattering light that passes through the stone. These diamonds fall outside of our grading range and, if submitted to be graded, would receive a Colored Diamond Identification and Origin Report, not a Colored Diamond Grading Report.

If the diamond you purchased didn’t come with a GIA grading report, you can still submit it for grading. The report would provide you with a scientific blueprint of your stone’s exact quality characteristics and may better explain what you are seeing.

For more information on the 4Cs, including color and clarity, visit:http://4cs.gia.edu/EN-US/the-diamond-4-cs.htm

There are also some Lab Notes that we’ve published on fancy whites if you’re interested:

-Fancy white, Summer 2000, G&G Lab Notes, p. 156: http://www.gia.edu/Summer-2000-Lab-Notes-Gems-Gemology

-Unusually large Fancy white diamond with whitish banding, Winter 2006, G&G Lab Notes, p. 262-263: http://www.gia.edu/Winter-2006-Lab-Notes-Gems-Gemology