I don't know if anyone else struggles with this but I'm having a bit of trouble with the darkness of the onion skin. Sometimes when I animate things that require a lot of detail and lines, it can get extremely cluttered and hard to see because of the similar colouring for the opacity of the first onion skin and the black lines. Maybe either switch the opacity up a little (a bit more transparent?) or add an option to change the opacity of the onion layers themselves.