It is a mish mash of color and icons that originates from several different mods out there... I got this one from another player on the discovery forums:
The problem is that the buying/selling screens are not aligned properly.
To install it go into your freelancer folder, then your discovery folder... find your interface folder and BACK IT UP FIRST. Then take the new interface folder and copy it over the one in your discovery folder. The only other issue I have with it is that sometimes the map takes a moment longer to load than you would expect
That link directs to the thread that states the only *officially approved* graphics mods are the lighting and hud-shift ones, however, the lighting one is definitely worth getting... (just as a side note)
As for the interface one(s), is there anywhere with more than just the one Kikatsu linked to? I know there's a few around and I want to have a look at them all and pick my fave since I've remembered about them now...
I did warn you about the buying/selling screen not being aligned properly. It is really an annoyance more than a game breaker, but I do not know how to fix it myself :/
Also if you mean the space background there, there might be alternate star field packs or something floating around, I have never looked into that though, so I can't help you there.