Answer: Nelly Moser is a jackmanii clematis, with pale mauve-pink flowers with a deep pink bar in the center of each sepal. Your medium purple with white underside could be C. jackmanii 'Mr. President' or C. x durandii ( a hybrid between jackmanii and integrifolia). There's a great collection of clematis pictures in the Roger Phillips 'Shrubs' book (ISBN# 0-679-7234-5). Perhaps a picture is worth a thousand guesses?
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