Jerry welcome to the forums! Not sure you're going to like the answer but here it it....
As of 8.2 Tableau serves up the background map tiles from either their company servers running OpenStreetMap, or if you select the Tableau Classic, you'll get the tiles from Urban Mapping (for free, at least until January, after that the picture is unclear, unless UM and T have come to a recent agreement). These two background map layers can NOT be formatted (font-wise) from within Tableau. However, both sources use a TMS file to send the meta data that tells the map server what to send back. Hacking either of these files will probably give you some control over fonts, but it is not a straightforward process. When I hacked the Urban Mapping TMS, I had to get a lot of help from Jake (great guy) because the labels and roads were grouped together, so I had to get the syntax needed to pull them apart and format them separately. While I did successfully get what I was looking for (darker roads that can be seen through filled maps), when 8.2 was released it broke the hack. So since this is a hack (not supported by Tableau), I can't really recommend hacking the TMS.
You do have the option of creating your own WMS server, formatting everything the way you want and then connecting to it instead of the out-of-the-box solution. alan.walker has had a great deal of success using this technique. It's a bit of work to create and maintain, but he can speak to that better than I can.
I can't really think of a workaround for the way you want 'highlighting' to work. That's the default behavior, and it just really is the way it is. There might be something you could do by hacking the XML, but again it's a hack, so buyer beware.
Sorry to be the bearer of bad news.
No worries. Thanks for telling me the bitter truth I didn't want to accept