I would not recommend changing the actual bootstrap CSS files. If you do not want to use Jako's first solution you can create a custom bootstrap style sheet with one of the available Bootstrap theme generator (Bootstrap theme generators). That way you can use 1 style sheet with all of the default Bootstrap CSS with just the one change to it that you want. With a Bootstrap theme generator you do not need to write any CSS. You only need to set the hex values for the color you want for the body (Scaffolding; bodyBackground).