Notepad++ highlight transparency

Solution 1:

  1. Go to Settings
  2. Click Style Configurator
  3. Under Language, select the appropriate language or Global Styles for all languages.
  4. Under Style, select Smart Highlighting.
  5. On Colour Style change the Background colour as you wish.

Solution 2:

Set all language specific backgrounds to black then set current line to the darkest blue and Smart Highlighting to the darkest gray.