I wouldn't make that a buying decision unless you shoot film. While the 17-40 has better colors, the 17-55 has much more relevant advantages in other areas (aperture, IS, zoom range etc)
The 17-55 is a much more satisfying lens on a crop cam than the 17-40L at wider apertures, indoors, for portraits. I did find the color and contrast of the 17-40L outdoors to be better straight from the camera.
