Blue logo is not visible on most of the backgrounds except on the last one. Should the background be changed or emphasize the logo different way?
I choose nr 4 because of that.
Yes i am having the same feeling about the background: It looks a bit "psycedelic" 
On the other hand, i think, it its a good idea to make the cover fit with the already existing books of this series.By the way:I see, my initial donation, seems to be the only one, they received yet.
Europecoin never ever asked anybody for a single cent and we never will.
But these guys are a third party, who showed engagement for our project and they are doing a honest work.
I would love to give them a nice picture about the friendliness or our community.
changing the world starts with generosity,
it does not even cost big money, to show some respect to their work:
YOU CAN SUPPORT THEIR WORK BY DONATING TO THEIR BTC ADDRESS:
DONATIONS TO

1CRLy4xUZbh9rj2GPANiNNBZGZKRKLYYwJ
thank you
have fun
Matthias ;-)