The easy way: Pick an alternative Color Scheme:
Preferences > Color Scheme > …pick one
The more complicated way: Edit the current color scheme file:
Preferences > Browse Packages > Color Scheme – Default > … edit the Color Scheme file you are using:
Looking at the structure of the XML, drill down into dict > settings > settings > dict >
Look for the key (or add it if it’s missing): lineHighlight. Add a string with an #RRGGBB or #RRGGBBAA format.