Reading my post I noticed a small but crucial mistake that may have prevented the correct understanding of my point. This is what meant:
I understand the reason why the minimal/base margins are displayed in gray and I also understand that we should have a visual difference between the minimal margins and the additional margins, but to me it would make mores sense if the additional margins had a lighter shade of gray. That way we would be able to see both margins and still differentiate between them.
Alternatively it would also be nice to have print preview function that simulates the actual printed page without the gray margins and with the eventual crop marks, mirrored edges and so on.
Does it make sense to anyone else?
I hope it makes more sense now.