They clutter up the interface. Why were they added? Was it that hard to figure out what could be resized? They'd be better if there was some discernible visual logic to them. Right now they are just slapped on top of the the resize zones like masking tape or something. They don't seem to end, or fit with each other and everything else how they should. Why the gap between the horizontal and vertical ones pictured? Why the overlap onto the menu bar at the top?
I tried to get them the same color as my classic theme background, but I couldn't get it somehow. Even if I did, there would be a bad transition between the main toolbar and the tracks.
Could we clean them up a bit, or add a checkbox in the theme editor to keep them from being displayed?