Bruce,
It's the inverse color of the 3D object, I doubt there is anything you can do about it. I imagine it's done as a visual cue to let the user know they clicked in there.
>I spent some time today trying various ideas on a grid to remove the black flicker one gets when one clicks on a vertical scrollbar. Naturally, I came up empty, since this is common to all scrollbars in all apps, as far as I can tell. I wonder why no one has ever resolved this? It doesn't affect functionality, but once you start noticing it, it's sort of aesthetically unappealing :) Anyone ever worked on this?