What you'll need:
Clear brow gel/clear mascara
An old brown eyeshadow or any shade that suits
Tweezers or anything that can be used to scrape the shadow
Most of us have old eyeshadows hanging around so you more than likely wont need to buy one.
What to do:
Use your tweezers to loosen some eyeshadow
Carefully pour eyeshadow into the gel
Replace wand and give the gel a good mix
You can add as much or as little as you want. You'll know when the gel is dark enough for your brows.
I didnt take photos of the process as I was in a rush but its so simple to do and works just as well as more expensive versions. I know MUA do a clear mascara for £1 and if you already own an old eyeshadow then your new tinted brow gel is a bargain!