Thanks, guys. Both of those approaches are better than the default swirl, IMO. I think I prefer the flat black to the blank white, personally.
But, neither really cuts into the GPU load. Even in the empty fog_genm.tga file, one can see the white background transition in intensity. So, I suppose all of the computation behind the animation of fog_genm.tga is something that the client does regardless of whether that image file actually has anything in it. Not especially surprising, on consideration. Is there a setting or client hex that turns that off?
BTW, my purpose here isn't really related to the aesthetics of the swirl. I have a slightly older laptop that I sometimes leave on the login screen to PWs, so that I have some idea whether my teammates have logged in. But, that laptop starts to heat up a bit and I would like to minimize that, just to prolong the life of the machine and its components (especially the battery).