Hi Ben,
Sorry it's taken so long to reply. Painting boats involves using a graphics editor like Photoshop or Gimp, then saving the files as a .dds
Templates can be found here: http://uhlhydroplanes.com/topic/217/hydrosim-paint-scheme-google-drive
If you look where your game is installed at HydroSim_Data\StreamingAssets\Teams you can see the file structure and names.
We're all on Discord, that's a better place to get faster communication!