I've beaten the game several times, but I get frustrated every time I r…

I've beaten the game several times, but I get frustrated every time I reach a level such as Mist Island and Lonely Iceberg. You can build a scout hut on most of the levels, and have them swim later on. I've been going back after swim to clean up all the black areas to get a better score on the "world explored" at the end of the game. However, in these levels (the ones I can think of off the top of my head) you cannot build a scout hut, so you can't get to the areas of black to clean it up. That also means you can't build a tower to get rid of more black area. Does anyone know of a way to get rid of the black? I've beaten the game and have ended up with 87% of the island explored. I know it's because of all the black areas that remain. If you can be of help, it would be great!