pretty easy to control. I found that if the surface of the wood is burnished smooth then you can control the depth of the color by applying heavy wet coats and allowing it to soak in or wiping it away quickly based upon how rich or dark of a hue that you desire. It will darken by shades with each application.
This is an R10 that I refinished using mahogany leather dye. I could've easily gotten a deeper red by applying additional coats:
Here's a stock that I stained for a flintlock that I built. I used a home brewed stain called "aqua-fortis" for this color. Just like the gunsmiths of yesteryear used to do. It gives a reddish hue to light colored woods such as maple or beech.