I played around with my svg file until I got the first object to be visible. It turns out that the fill attribute for each object was set to black, 000000. So I selected all the objects in Inkscape and set the fill to 010101 and svg2lay processed all the objects.
The bg.png files are all black. Is that correct?
Do I need to specify colors? The pngs that were created are all black (well, 010101) foregrounds on transparent backgrounds. They look OK to me, but I don't have the latest MESS with Top Gun included to see what they look like in the game.