In the Spine-Unity runtime, there is no built-in functionality to serialize and save changes made to a skeleton, such as vertex color changes, back into a Spine file. The runtime is designed to render and animate skeletons, not to modify and save them. Any changes you make to the skeleton, such as vertex color adjustments, are typically applied at runtime and are not persisted.

To save such changes, you would need to implement your own system to store the necessary data (e.g., vertex color changes) separately from the Spine skeleton. You can then reapply these changes each time the skeleton is loaded. This approach involves saving the state of your modifications (like vertex colors) in a format of your choice (e.g., JSON, XML, or a custom format) and applying them to the skeleton when needed.

@suanLoBeach Vertex color is set via attachment color. There is no per-vertex-color in Spine's skeleton format, and you can't e.g. write a Spine Editor plugin to edit and serialize additional data.

You can always write Unity editor scripts and serialize your own asset files however. You can freely modify the spine-unity source-code however you need.