So, there’s this:
And i want to set transparency: palette entry to 255 like so:
But when I’m already inside the project, so it’s re-setting it.
I just can’t find it in any of the tools/menus:
Nor in kb shortcuts:
Would be cool, i think, if we could set the transparent color via right click.
OMG! I’m so blind! Thank you very much! Like, OMG!
Who knew this tool existed? Not a blind person! 
I kind of understand now why it currently doesn’t have a kb shortcut. It looks to be a software and UX design problem. I’m guessing there are more of these but not enough to need a revamp. Oh, well. Anyway, again, Thank you!
People from the future, just for easier access, this is the button Mathias is talking about:
ahahaa, glad that helped!
Within a single layer you can change the transparency, too. Double click on a layer:
But having different transparent colors for layers should only be done if required for good reason. It can make things more complicated.
