Since a VAF filter for the 50D is no option at the moment, using a different Software might help too.
I got similar results when I open my DNG images with Google Picasa, but by opening them with Lightroom 4 I got rid of the colorfull borders.
Probably because Picasa's debayering sucks.
So if you aren't using ACR or Lightroom already, you might want to give them a try.