Good: These are the resources that you consider to be in a 'good' state-- no attention required. Using the color drop-down, you can change what color these resources show up as on graphs and reports.
Warning: These are the resources that you consider to be in a 'warning' state. Too much down time and a resource will slip into this 'warning' state. You can set the threshold availability % using the setting here. In a 99.9% uptime environment, this should be set to 99.9%. This way only all-success resources will show in a 'Good' state.
Bad: These are the resources that you consider to be in a 'bad' state. This is the worst state a resource can be in and is never a color we wish to see resources in. You can set the threshold availability % for this as well. Anything below this threshold is in a 'Bad' state, and will be of this color on graphs and reports.
Default Availability Days: This is the number of days the Availability % in the resources list is based off of.