I second the idea that it not be the default. This isn't because I don't like it (I don't though as it makes it very hard to read) but because to disable it you have to find the original background color and reset that yourself and for some of the monks less familiar with html and css this can, and proably will, cause a bit of confusion.

So to help a few people along the way the css needed to remove highlighting (on the default themes and NN only) are:

tr.post_head, tr.highlight { background-color: <color>; }
 where color is: 
  #FFF /* Blue/Green Web-Safe and Red */ 
  #010D5D /* JBlue */
  #eee /* Perl-Blue */

or for the NightShift and Dark themes just:
tr.highlight { background-color: #000; }
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