Hey Steven,
I have some examples from the 15mm Heliar. I can post them next week for you. There is one picture up on my website that shows the color shift in an article I wrote about switching from an M6 to an M9. It is just a picture from inside my art studio at the bottom of the article.
The shift is heavy in the bottom left corner. I have tried setting the camera to the WATE preset or the 21, but the shift is still there. If the image is converted to BW its is not a problem. But depends on your shooting style.
I would be inclined to advise buying a used 21mm Elmarit. You can get them for less than $2500. Here is one at Photo Village, for $2300, just to give you an idea.
You can save some money buy using the Voigtlaner view finder. I have used it in the past with the 21mm Elmarit with no issue.
http://photovillage.com/product.php?productid=2772&cat=0&page=1
http://www.adammarelliphoto.com/?p=71
Best-Adam