When it comes to black fences, they're generally made of wrought iron or painted steel. And when it comes to wooden fences, they're generally treated with a clearcoat to let the natural wood show through or they're painted white. But there's lots of reason to use black wooden fences:
The black can create a taut, modern look and wood is easy to work with for home DIY-ers. If you aren't too keen on the maintenance involved with a painted fence, consider a Shou-Sugi-Ban finish.
Images: Botanus via Studio G, Perfection Fence, Chahrour Huhtilainen A+D, Le Boeuf, Home Works