krammor The area you boxed in red should have nothing to do with that black border. That is basically what is happening because you have the Premultiply alpha (预乘Alpha) enabled.
If you don't know what Premultiply alpha is for in the first place, the following video may help. (Maybe your asset is not used in Unity, however the advantages of using premultipllied alpha images are basically the same in other runtimes.):
【[spine-unity] 常见导入问题解答】 【精准空降到 01:47】 https://www.bilibili.com/video/BV1BD4y1Y7By/?share_source=copy_web&t=107
If the texture atlas page has not been compressed or otherwise processed after being packed by Spine, it will always unpack cleanly, even if it is a premultiplied alpha image. If you want to make sure it works correctly, you can try unpacking Spineboy's texture atlas page using the following .zip file:
As far as I've tested, unpacking the pre-multiplied alpha image works fine in the latest version, so unfortunately I don't have any specific advice for your problem.
