If you encounter point clouds that are incorrectly colored black, you may be linking against OpenCV compiled with the -ffast-math flag. This problem is described in http://pointclouds.org/news/ffast-math.html

Fix:
- go to your OpenCV build directory 
- sudo make uninstall 
- remove old OpenCV files and download latest from sourceforge or update your svn if you use developer trunk
- use cmake-gui to configure your installation and verify that "use fast-math" option is not checked (you can verify it looking at the flags to compile the release version)
- sudo make install


Thanks to Walter Lucetti for providing these instructions.