There are no grades for anemones. Sounds like marketing BS to me. What kind of anemone are you in the market for?
BTAs seem to have the most hype surrounding them. I wouldn't trust any of it. The key is to find a reputable seller who knows the lineage of the nem you're purchasing -- this is assuming you're looking for a high-end BTA like an inferno, Colorado Sunburst, lemondrop, etc.
All other anemones aren't captive-raised so they don't have any lineage associated with them, nor do they have any sort of color or quality grading.