You can counteract this by reducing the contrast and brightening the image. Paint Shop Pro. You can also add a matrix or a color shade to the image. This can give a very professional look. You could for example add a company logo to your background.
People can be pig-headed.
Sometimes they just don't want to see background images. Sometimes they have no need for images, loading them takes too much time. These people will alter the settings of their browser. You should take the effects into account. You cannot think of everything, but try some possibilities.