This clematis is almost a pearly white but it seems to have a very faint pale mauve coloring around the edges on the younger flowers. I am also adding a second pic with more mature flowering.
ID Please
Looks like 'Snow Queen'
http://davesgarden.com/guides/pf/go/65653/
Thank you! I think you are absolutely right. Not sure how I missed that one. Now all I have to do is find someone who sells it up here.