missing background-color

I need to know WHEN the validator started issuing WARNINGS for missing background-color.  Please do NOT tell me when it was added to the standard, I have SEVERAL archived editions of an online newspaper that were checked, and the validator said "no errors or warnings found".  I need to attach a note explaining that the warnings started appearing on such and such a date, and that prior issues are now showing a warning that never existed.

JohnV
Head Honcho
The Zone Gazette