If you are limited to that jacket, then definitely go with horn over the others. You want to make the most use out of what you've got. MOP really only makes sense in spring and summer, and either MOP or silver will make it much more conspicuous that you're wearing the same jacket again and again. They are also much more casual.
Part of the reason you should stay away from khakis is precisely to make it less apparent the jacket is orphaned from a suit. Paired with pants so casual and rough-and-tumble, the jacket is even more slick and smooth in contrast.
That makes a lot of sense on both fronts. May I ask what type of trousers you'd suggest? I guess light gray flannels, but what else might I do?