I forgot the forum disables edits after some time.
I was going to emphaisze the part where this is the solution if you want to stay with the Linear color space.
But part of the solution is to change the settings in Edit > Preferences > Spine

straight alpha settings:

Using these settings makes sure future assets are imported correctly.
For new users or passers-by, just switching the project's color space to Gamma is the quickest way to a solution. But if it's an existing project with lots of stuff in it, that's a no go.
There's a lot more to describe about either setting.
I'll just make a blog post about that in my own time.