Firefox - from the menu bar - TOOLS > OPTIONS > GENERAL > COLORS > change background color, click always, click ok. This will change background for every web site but easy to on/off.
Internet Explorer - from the menu bar - TOOLS > INTERNET OPTIONS > COLORS (on first page), uncheck 'Use Windows Colors', pick your background (or whatever) color, click ok.
you can use this to change background, text, etc. colors. You may need to change back for other web sites but very easy to do.