I’ve found an optimal (I think) solution of this problem, at least for Mozilla FF: just made these colored blocks semi-transparent.

  1. Disable AVAST self-protection
  2. Edit file …\Avast5\WebRep\FF\content\hover.css: add the next string to #wrcHoverDiv (1st block there)

opacity: 0.5;

  1. Enable self-protection.
  2. Restart FF.

Small green thumb-ups, -downs, -etc. are png-images and can be edited in any editor for raster graphics. Look at …\Avast5\WebRep\FF\content\common\skin\img\se_icn_[color].png (or …\Avast5\WebRep\IE\templates\img\se_icn_[color].png for IE).