[Technical Question] - How does the political map work?

I really like the aesthetic of the game, and in the future, I would like to create a fantasy map in the style of EU4. No mods or anything more complex—purely art. To mimic the EU4 map effect, I tried to overlay a grey map with a cloud effect, and on top of that, I wanted to place a layer with the countries, with 85% coverage. However, the effect is not even close to EU4. To figure things out, I used color samples from the game files, but I am still struggling to achieve the proper shade in Photoshop.

As I understand it, in the game, under the colors of the countries, there is a map (which I cannot find in the files), and the countries are generated on top using specific, predefined settings that I also cannot find.

Does anybody know how the system of the political map works and where I can find the resources?