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Good quesion @newtechblog.

Green means that the value has increased as compared to 1-week, 4-weeks, 12-weeks or 1-year.

If we take Amicable Numbers, the GRC per 1k RAC has increased by 1.1% since last week but has lost 5.5% since 4 weeks.

I hope this answers your question.

ok...it is understood

No, because the same machine won't usually produce the same RAC on two different projects. I recommend checking out quickmag to help you pick between projects.
http://grcquickmag.hopto.org/cgi-bin/script.cgi