Whenever I get new reputation events, badges, or comments I end up scrolling too far because the highlight is too light. See for example in this image:
The regular background is white (#FFFFFF) and the highlight is very light blue (#F0FBFF). At some angles, they are the same color.
I don't know if the color can be changed enough to make a difference without messing with the site icons, but it should be possible to add a colored left border if that is the case.