By default, the background color for typing in Word is bright white. For some people, myself included, this bright white can cause eye fatigue after a while. So, I've found that changing from the white to a gray background can help.
To change your background color, open up your normal.dotm file to edit it. Go to the Page Layout tab in the ribbon and click on the Page Color button. There, you can choose a color more to your liking. Be sure to save your normal file.
Now that your eyes have thanked you, there is another consideration. If you print this out, it might print out the colored background. There are times you may find this desirable, but most of the time, you won't.
To fix this, go to the File tab, then choose option. Click on the Display button on the left side menu. Ensure that "Print background color and images" is unchecked.
Now, when you print, it will ignore the gray background. Of course, if you want to actually print a background in the future, you will need to check this box.
Lastly, when you re-open Word, it might not display your new, colored background. To fix this, you will probably need to display background content. Go to the File tab, choose options, and then choose Advanced from the options on the left. Scroll down and check the box for "Show background colors and images in Print Layout view".