Help! Changing background colour

Is there a way to change the background layer colour once you've started a document? When I first created my document (in PS CS2, if that makes a difference) it automatically set my background colour as sepia, instead of white.
I'm now working on a painting and just realised that I can't use white; PS is calling this sepia colour white, and I can't get anything lighter.
Is there a way to fix this? I've done it on a few pictures now and I don't want to have to start everything over.

Please?

Edit:
I've just tried making a new document with a white background layer and the same thing still happens! What is this?! I'm sure this can't be right! I'm on some sort of sepia scale; I can't even do grays. *desperate*

A strange sounding problem.

What happens when you press the letter D on your keyboard?

This should set the background colour to its default colour, which is white.

What colour is in the small overlapping squares at the bottom of the PS tool bar?

The foreground one should be black and the background one should be white after you press the letter D.

Double click on the background square and see what the colour values are.

If it is really white, the RGB values should all read as 255. If it is Sepia, it should be something else.

Can you upload a sample image which shows your problem? I use this site,

http://www.pixentral.com/

It was anything like that, the RGB values were all reading 255 and the background on the overlapping squares was sepia. That's why I was having so much trouble.

I finally managed to fix it though, after playing around with the monitor settings. Apparently it was something to do with that. :o

Thanks so much for the help though!