I always reconed Kerbal was inspired by http://www.agi.com/products/stk/ , heavily used in the space industry

Or, third option, "there's only a few decent ways to represent orbits on a graphic".

The colour schemes are very similar though. There are many colour schemes one could choose.

I know that the main author of KSP was a big fan of Orbiter before making KSP, and I think he was aware of other astronomy software.

I want, by the way, an interactive map of the solar system, complete with known spacecraft, with the same UI as the KSP map. I've never met anything quite as good at visualising planetary systems.

I haven't found one.