Black is indeed quite rare in nature, but that's not the problem.

It's indeed helpful to create contrast, but it simply fits into very few environments and a large share of darkness in patterns stands out even at long range if the background is light.

One key problem with dark/black camouflage (even if only partial) is that it's relatively easy to see in low light vision because it doesn't reflect the low light as other surfaces.


Overall, there are good reasons for and against black, and two cases when it's right and when not:

* Black is right if soldiers can best (only) really hide themselves in shadows.
This is true in very closed terrain where short range (up to 100m) camouflage is important and long-range camouflage less important. This has also an impact on the size of the pattern.

* Black is completely wrong in, well, the opposite case. Long lines of sight, long range combat, camouflage possible even outside of shadows.
Black is also wrong if the vegetation allows for effective hiding on open terrain, like on high grass.

I wouldn't just change the pattern to improve camouflage anyway; we need to go to 3D camouflaging.
Examples:
"Camouflage system"
http://www.pri.uk.com/html/clothingthumbs.html#systems2
and this
http://soldiersystems.net/2009/06/11/boonie/

It could even look orderly in garrison - and be sliced up along marked lines for deployment (and field training).

I would use such camo on arms, shoulders and chest.