Try beard dye. Light brown should be dark enough for you, and it won't be too noticeable if you get it on your skin. I used to dye my beard before it started coming in dark on its own. Put the dye on for just a few minutes, wash it off, and do it again. It may take a few tries. If you do it multiple times, it makes it less likely to stain your skin, and you have a better chance of getting full coverage.