I have pretty good luck with a good oil based stain, which I add to or take away from the mix till the colors suit me then allow to dry for a week or so and then apply multiple coats of teak oil or even Tung Oil varnish for sealing. I have done this with various sized handles for more than 30 years successfully.
Lots of old timers on the farms hereabouts soak their axes in a bucket of coal oil for a few days before use every season. The oils penetrate the handles, swell everything to tightness and shed water. According to the old black powder shooters who used wooden ramrods around here, the coal oil lubricates the wood fibers so that they then can slide against one another without cracking or breaking internally. They claim that a wooden ramrod soaked in coal oil almost can't be broken in use because it can be bent nearly double without being brittle enough to break. The coal oil soaking makes an axe handle look sort of used and abused to me. But I have friends who have done this for 40 years and get enormous use from a handle.