What does this mean exactly?

It means that you can have (for instance) one Uptime Monitoring Professional package, and be on the Free Blacklist Monitoring package. You can still use the Partial White Labeling that comes along with the Uptime Monitoring Professional package on any of your Blacklist Monitoring reports.

Basically, the White Label system works system wide, and you only need at least one package which has it enabled, so you can start using it on all of your reports.

What if I have a package with Partial White Label and a package with Full White Label?

The highest level of white labeling will always take priority, and will always affect all of your reports, so in the case described above you’d have Full White Labeling enabled for your entire account and all of your reports.