I've run across shoe polish before. I use it on sporting rifle stocks. It's easy to touch up and does a good job, keeping the weather out.
I 've also seen it used on birch hand guards, to make them look like walnut. You will want to be careful, takeing it off though. It penetrates into the pores and can go quite deep. If there are cartouches, you are trying to save, it could be a problem. I usually strip it off with ammonia as well.
The last time I used it, was on a Boyds replacement stock, for a Garand. When it's heated up to liquid form and a bit of BLO
and alcohol mixed in, it can look quite good. If done properly, the grain of the wood will be slightly enhanced but well sealed.