How can I stop this happening?
 

I seem to always get colour interference bands. What's causing that?

http://thumbnails109.imagebam.com/39...2390403871.jpg

That's a moire pattern, your scanner is trying to make sense of images printed as dots.

Try scanning at a different resolution or check your scanner's set up for a "de-moire" or "de-screen" setting.

http://www.scantips.com/basics6c.html

I can confirm Hugh's advice from my own experience. First try: use the de-screen option when available. Next: try a different resolution. That can make a great difference on the presence of moiré. Last: resize.

higher res did it! Thanks :)