If I understood your original problem report, I think it is just a matter of changing how you use your tools a little. The statement "Specifically, even without gaps, the blue would fill the whole page" was suggesting an unconstrained floodfill. I apologize if I misread your original request.

If you want to do something like https://cartographersguild.com/showt...t=33087&page=2 or https://cartographersguild.com/album.php?albumid=4578 or https://cartographersguild.com/showthread.php?t=29412 or https://cartographersguild.com/showthread.php?t=18120 then you can just run a basic paint program and paint black and white things and let Wilbur generate 3Dish things for you. If you wanted to keep basic 2D painting with layers to create individual maps and then assemble them onto a globe surface using any number of GIS tools like QGIS that can help you. A more primitive tool like Fractal Terrains from ProFantasy can also do this sort of things, but it takes a bit of fiddling about to get good results.