some thumbs hardly visible on pager

[(none)]

I've recently moved to KDE 3.5, but this also annoyed me with the 3.4
version ...

I'm using a rather dark desktop, and for many apps it's quite hard to
see which virtual desktop the window is on (see attached screenshot).

(If you don't get what I mean, try to find the terminals I have opened.
They are visible, but quite hard to find on the pager.)

I haven't found an option in any of the KDE menus to improve this behavior.
If there is some config file entry that can help this, I'd be glad to
receive a hint on it.
If not, could it be possible to brighten the thumbnails so they become
more distinguishable or draw some kind of bounding box so I can at least
see the outlines of the windows?