'Soft' versus 'hard' backgrounds...
Importance of backgrounds cannot be underestimated. They make the impression (first impression is the last impression, you know! :-)), they highlight the text/images, they attract readers, and they create an environment related to the subject.
Usually, backgrounds are 'soft' - so that they do not interfere with reading. Of course, a "background" has to be "back-ground" only and should not override the subject matter.
Here are a couple of examples of 'soft' backgrounds:
But, there are sometimes, when a designer needs a "hard" background. Such instances could be when the main text/subject matter is 'short and sweet' or the subject itself demands prominent shapes/colors.
You can consider the following ones "hard" backgrounds.
Such backgrounds, when used appropriately and creatively, can give impressive outputs. On the contrary, when not used properly, they can spoil the overall look, too.