rhm

Leather won't stain your pants, but there are a lot of things people put on leather, and these will stain. A new Brooks saddle, kept dry, is probably okay; the people at Brooks know how to stain leather. But if it gets wet, or someone has treated it with too much proofide or neatsfoot oil or shoe polish, it will definitely stain. The best way to avoid this is to get a natural colored saddle. Whether that's called "honey" or "brown" is another question; I think what was called "brown" once is called "honey" now, and the ones they call "brown" now are stained to get that color.

Don't listen too much to those who tell you how to "break in" a saddle. If you ride on it, it will gradually change as it gradually wears out. Ideally the trajectory from a new saddle to a worn out one should take something like 50 years or somewhere above 50,000 miles. Treating it with neatsfoot oil or a lot of proofide (or a hammer, or olive oil, or... well, pretty much too much of anything) will reduce those numbers. The more you treat it, the more you reduce them. I've seen saddles ruined with less than a thousand miles of riding.

Proofide is good stuff, when used as needed. If used unnecessarily, not so much.