So this is another quickie from Dynamic Drive and very easy to implement.
To implement this you simply have to add the following to your page either as an include or just to the page somewhere.
Once that is in place you then need to add the following lines to your page.
Oh and be sure you gave your form an id and then put the right id into those lines.
Once that is there and in place you are basically done.
What you can now do is if you have a user preference section you can actually allow the enabling and disabling of this option, as well as allowing them to select the color for the background this of course giving the user more control over how they work.
This is actually something I’ve recently implemented, provided the user variable is set to true I active the two lines which assign the event to the form and I dynamically set the color the user has selected.