I’m curious if it’s possible to set default settings for onion skin settings? I always use specific colours and opacity when using onion skin so I’m having to set that every time I create a new grease pencil object. It would be great to be able to set and forget this setting.
Start with a New File … File > New > General
I would set up a new workspace ( top bar + )
In there I would set up an empty GP scene, and add and or change the settings you wish to use…
Then use @walt1 suggestion of Saving as a startup file…