Can you send provide me with the image file that you edited? I assume it was image 98, just so I can see if I can help you with the black outline issue. As well keep in mind that, because Wildshadow was extremely unorganized, I'm very certain that other tiles exist within other image files.
Edit: Actually reviewing your screenshots, I believe it's because you forgot to save the file with transparency. Make sure your editing software supports this ability. So reopen the file, apply your changes, and then save it as a transparent .png. I can't explain how to do it if you don't know, but there are plenty of tutorials on the internet.