RTF is a global modification that replaces all towns in the game.

If you are working in Paint.NET, you need to save the icons with the A8R8G8B8 parameters. And if you are recoloring textures, you need to generate Mip Maps so that the textures don't appear pixelated (if you save the icon this way, it will be blurry, and at low quality, it will become distorted).