Okay. I tried to use N3DCamera's -renderToTIFF method.
What I got was an image which was 24 bit rgba. The problem is that the
shape in the picture is all black, while the rest of the image is transparent.
The effect is like a silhouette.
The lights I'm using are on at decent levels, so I know it's not that. And, the image looks fine on screen. (What I did was I modified the Teapot Backspace module so that it will render a number of frames photorealistically and save them as JPEG-compressed tiffs in an .anim folder.. I know, I should use an N3DMovieCamera, but I thought I'd start slow.)