This is wrong. You can check it with simple scenario
0% - 50% available traffic used - green
51% - 75% available traffic used - yellow
76% - 100% available traffic used - red
The truth is
green - a class the actual rate of which is equal or less than limit-at.
yellow - a class the actual rate of which is greater than limit-at and equal or less than max-limit.
red - a class the actual rate of which exceeds max-limit.
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