The following suggestion came up on a forum a few days ago, and I think it’s a very good idea so I’m reproducing it here.
There’s a setting in Windows that allows the user to set the background colour of application windows (it can also be set individually in Internet Explorer or Firefox). Why is this important? Because it means that if you’ve developed a web site with a white background (the default for modern browsers, in Windows at least) without explicitly setting the background colour to white (either using CSS or setting the COLOR property of the body element), then it’s likely that a proportion of your visitors are seeing it with a different-colour background.
So what’s the idea? Set your own browser’s default background colour to something other than white (I use light blue). This will alert you if you ever forget to set the background colour for your site.
While it could be argued that these people have changed their background colour for a reason, it’s also possible that having the wrong background colour could render your site totally illegible. And also, those users who insist on using their own colours can still force the browser to use them.
As an interesting side-effect, you’ll find as you browse the web just how many sites have this problem — I come across a few every single day.