Roofing tar and mineral spirits. The more tar, darker the stain, less tar lighter stain. Been doing this for years and years.
one gallon of tar will last a few years. Just mix well and when you mix make sure you do enough for the whole project to get same color. Tar is only about 5 dollars a can and mineral spirits is a few bucks for a half gallon. Way cheaper then the ready made.
Just wanted to share in case some of you have never done this before. Learned it from an old timer.