I have some semi transparent objects in my spine project.
When I was exporting them with pre-multiplied alpha and unity was set to use gamma colour space everything looked fine.
I need to use linear colour space so I followed the instructions in the warning and re-exported the spine project with pre-multiplied alpha disabled. I also enabled the 'straight alpha texture' option on the materials. I found that the colours were all messed up until I also set the textures to sRGB in the import settings.
Now all of the opaque objects are looking correct but the semi transparent objects aren't, I'm not sure what is wrong.
This is what it looks like in spine (and how it looked in unity with PMA):
This is what it now looks like in unity:
As you can see the shape and the colour/transparency are both wrong.
The transparent part looks fine in the texture itself so the problem doesn't appear to be in the export.