Highlight counties or regions on google maps

I am using Wordpress CMS and have maps that we dynamically generate the 'log & Lat' this is got from a custom field. The PHP and JS are created on 1 PHP file using standard google calls. AKA not being generated by some plugin.

Part 1
I would like the map to be able to highlight the current Country/region selected on the map. A lighter shade.


For instance, if Paris is the centred location on the map, I would like France to appear as a lighter shade than the rest of the map.