I just looked at this. In my version (1.9.13.0), the drop down menus are not transparent when dropped down. In any case, if you set the page width to full the transparancy disappears. Does that help?
The file seems to be called "alias" and is in C:\Program Files (x86)\Scrivener\resources\toolbox\namestool\alias, but it's semi-encrypted so it won't do you much good.