Colonies with active shields, or outside of your allowed level range, have a red border on their icon shown in the box that pops up when you click on a system whilst in the Galaxy View. Green border means attackable.
Just above your list of in game friends there is a location navigation bar which reads like this:
Galaxy > Solar System Name (X,Y) > Planet Name
If you click Solar System Name the view will zoom out to the Solar System view. Clicking on Galaxy will zoom out to Galaxy view centered on the current Solar System.
That’s 2 out of 3 covered. I can’t help with the destroyed colony issue though sorry.