From HP
"The icon displayed does not take into account the number of non-revs listed. When making your determination as to how a flight looks remember to take into account your boarding priority: SA1P, SA2P, SA3P or SA4P
Less than 80% - the flight looks great for non-revenue passengers of all boarding priorities.
80% to 90% - the flight looks good for all non-revenue passengers. If you are an SA4P passenger, take into account the total number of non-revs listed. A large number of non-revs will decrease your chances of having a seat on this flight.
90% to 95% - the flight looks ok. If you are an SA3P or SA4P passenger, take into account the total number of non-revs listed. A large number of non-revs will decrease your chances of having a seat on the flight. SA2P passengers may want to upgrade to SA1P.
Over 95% - this flight looks bad and is not recommended for all non-revenue passengers. You should consider trying another flight."
Hope that helps.