Don't worry, you're not sounding stupid at all. This is apparently a mistake on our part. We are revamping the entire manual which should be completed some time in April, but let me see if I can clear this up for you.
* Green means you have full access rights and therefore everything should come back properly.
* Yellow means a kind of Partial Privileges. This means you have some access to the remote registry, but not enough to access portions needed to retrieve certain items such as Software.
* Red means the computer is either off or not connected to the network any longer. Each computer is pinged before a scan and if there is no answer, you will see a red icon.
Note you can also look in the "Last Scan / Scan Status" column in the Primary tab to see more useful information. You can also just click on a machine and see this same info at the bottom of the NEWT Pro window.