It's not quite finished, but I did come up with a solution that I think solves the two tone problem and still creates a nice sweater.
I added ribbing. The entire sweater was supposed to be worked in a completely flat stitch (in what is called stockinette stitch). Here is the original pattern, with a picture.
Here is my version:
The ribbing masks the shift in hues. You can see it in this close- up with flash:
But I bet you couldn't tell in the sunshine picture, could you? I also added the colorwork on the sleeves, since the new cream color began there as well. The break up of the new cream with the pink helps hide the slight difference.
As an added bonus, the original cream color ended just below the bustline, and starting the ribbing there actually creates a very flattering silhouette.
I'm quite pleased with the result, and I'm not at all upset that the colors didn't match, because it forced me to use my creativity. Now I'm itching to design even more sweaters!