Has to be dark enough, but not so dark you can't see anything.
I really like the cliffs; unfortunately a lot of the bottom will be covered by a flat black area for the text. As it will be published in several languages, all text must be in black. This is because the text is done on a separate printing plate which can then be replaced to translate it. However, I have discovered it will be OK to have white text on a black background here. A pale area at the bottom would rather have spoiled the effect.