Uh. I wouldn't suggest using something like shoe polish on CWD tack. You may as well just spray paint the thing at that point. Just keep oiling it. Like other people have said, don't expect to get it dark automatically: if you're not going to a show, having matching tack shouldn't be that much of an issue. Just keep riding with the bridle and clean it regularly, oiling it afterwards. I've found that my tack will darken more with use and care rather than simply attempting to over saturate it with oil or leather conditioner.

I have two CWD saddles and my brown one started out very light, originally: even with oiling/conditioning, it was light. But the more I used it and cleaned it and conditioned it, the darker it got. So I guess that's my experience with CWD products. Don't try to darken it all in one go. Just let it happen over time.

“There's a lot about discovering who you are and how difficult that is, and it never stops.”
- Libba Bray