Using good imaging software (ex. Photoshop) will help with fixing color problems.

I also have a Canon and the background on it is white, I prefer a black background myself. I took the plastic black piece off my old one and use it with the Canon now.

It sounds like you've tried the obvious using white paper. Scanning and getting the colors right can be tricky sometimes. Have you tried playing around with the brightness/contrast settings and any others your scanner uses?

I would try that and see if it helps.