I guess it is a general problem with 100% width footers: if content is smaller than 100% browser height - there will be space under your footer visible. So if you don't specify body bg color, it will look white on large monitors. You don't have to use 100% width footer. You can make it only the width of your main container. But then you have to specify the same body color as the bottom color line.
Many pages have this behavior when content is not enough...! you see, height in browsers is a big matter (till css3)Also is not advisable to set a background color other than white.