It's talking about reserve coverage required vs available. Once the monthly schedules have been awarded and posted in icrew you can view a matrix for the month showing each day's # of required reserves and the # actually available for that day. Any time the available exceeds required the number will be in blue, if it is exactly equal or required exceeds available the number will be black. Where is matters is the ability, or lack thereof, to manipulate your schedule. In order to drop a trip or reserve day(s) the days(s) you want to drop must be blue. Swapping is somewhat more complicated as you can swap from negative days to negative days as long as you are swapping into more negative days. You cannot swap from days of bad coverage into days of good coverage.