How do I make good looking 2d map borders in a widget?

Info/intro
I have this map with multiple poi’s, it’s pannable, zoomable, and procedural, it’s 2d in a widget.

Info
I’ve already written code to create the delauney triangulation and voronoi diagram (I want to use the voronoi diagram) to create clean looking borders for different “nations” on the map. So it looks like this when I draw the lines (the current ones are just debugging)

Problem
…But just drawing the lines doesn’t look good at all. I want to achieve something much more artistic, like shading in the borders based on who controls it.

Constraints
How can I shade specific areas (like cells in a voronoi diagram), and leave others blank? How can I do that dynamically as systems change who control them? (not from a code perspective, I’m familiar with coding just not materials or masking or whatever I need for this) And does anyone have any better ideas for how to make a map concept like mine look better?