I always thought those pale-blue disappearing concentric circles were just to give you an appreciation that you are indeed moving relative to the planet.
In that sense, it plays the same role as the gradually accelerating sets of lines left and right of the cockpit in SC.
My understanding is that given the large distances that we have to travel in SC, sometimes it can seem that we're not moving at all because every other object is too far for us to appreciate, so these UI elements are here to confirm we are indeed moving.
But I could be completely wrong, it could be the gravity well.
The dark blue single circle is indeed showing the orbital cruise limit.