You can wipe the olive oil on with a cloth or use a paint brush. I have never worried about what color my saddle is, I don't show, so I can't answer that. As long as it is "leather" (some shade of brown) colored, I'm happy.
I ride in the rain, wind, snow, even been out in a thunderstorm half way up a mountain.
I second riding bareback if you can. I use leather cleaner and conditioner in one. Forget the brand, its amber colored liquid in a spray bottle. Works great, and I have tack 10+ years old that has been used heavily(and soaked in water/sweat frequently) that is still in great shape. I only treat it if it has gotten dirty, wet, sweaty or looks dry.