I've had what's maybe a bug in 1.5.2 and it's the same under 1.7. When I load OBJ files using the ObjectFile loader most of the materials don't load, so I'm missing colours. If I load the same OBJ file with MeshLab it's fine.
Has anyone else experienced this? mtl and obj files are in the same directory, it gets some colours so it must be reading it. Have tried with quite a few OBJ files from different sources.