This is quite a good study by Natick for the effectiveness of a range of camouflage patterns

http://www.scribd.com/doc/19823845/Photosimulation-Camouflage-Detection-Test

http://soldiersystems.net/2009/09/18/natick-camo-study-making-sense-part-ii/

The Natick results were described by a retired UK Special Forces Warrant Officer, "Nothing earth shattering; desert s@&* works great in the desert and green s@&* works great in the green area.".

As for the current US Army issue UCP or Universal Camouflage Pattern, it doesn't seem to be at all Universal since it doesn't work well in either desert or arid regions or work well in woodland either as well.

The so called Digital camouflage (multicam, spec4, UCP etc) is nothing really more than just a fashion statement or an attempt to make the camoflauge look more modern (to todays electronic gaming generation) even though digital camouflage materials has been around for more than 3000 years.