Hi supasam and welcome to the Q&A Board!
The answer to your question is, unfortunately, no. You can add a tone to your photos, such as sepia, during the editing process but can't restore full color.
It's easy to mistakenly change settings on digital cameras without realizing it. I have my display set to show settings and mode information. I don't always remember but do try to check the settings before taking photos.
As an aside, if you use the My Colors feature, make sure Save Original is set in the Rec. Mode accessed via the Menu button. The Save Original only appears in the menu when you camera is in My Colors mode. When you take a shot, two images are saved to the memory card: one with the My Color effect applied, and one that is a full color version.
http://web.canon.jp/Imaging/pss2is/301-e.htmlNot all digital cameras have this feature and it doesn't work when the Black and White setting is selected.