Hello,
Someone had asked about genlocking the background in Im3.0, so I
decided to check it out. What I found was that the background didn't
become transparent until I loaded a backdrop picture, which was one entire
picture using the color 0 register (the actual color of the register
doesn't matter) into the global settings in the action editor. Low and
behold – transparent and I'm even using Opalvision. Hope it helps.
BP