Black and gray pixels remain when You make a ship name first and than delete your black background. That's caused by too low Tolerance factor. Even if You incrase it, your inscription will cook like crap after all. I always delete tke background first and than make proper inscription with ship name.
Sometimes I'm using Transparency to have partialy transparent nameplate, some Feather also have good effects. All the scrathes for abandoned, old ships for example I'm doing via Clouds render. It's different story and a little bit complicated..