This one popped up in my garden about 4 or 5 years ago.  It is a natural hybrid from 'Candida'  <-which a large pure white, and 'Jackmanii'<- which is a deep dark purple!

I found a seedling today that I have no idea what color it will be, or what traits it will have.  I wont know until it blooms in around 3 years!

If you do not care what color you will get then starting them from seed is the way to go.... if you have the patience needed to wait!!

Clematis from seed is a challenge at best!  Especially with the hybrid types. All named varieties and cultivars are clones, which are started from cuttings.  Propagating from cuttings ensures that the new vines will be exactly identical to the parent plant. 

There are a few yellow pagoda flowering types that are easily grown from see, but these tend to be very gregarious and will bloom the first year if the seeds are started early.  The problem with these clematis is that they are invasive and will seed themselve to the  point that you will have no more room for anything else.  'Radar Love'  is one that should be avoided.

From seed, there is no guarantee that the offspring will be like the parent. 

If you would like to have a purple one then you should look around your neighborhood to see if anyone has one.  Then knock on the door and ask if you could take a cutting from it.  In most cases the neighbor would be more then willing to give you a few. 

To start them from cuttings: insert the cuttings into a pot with good quality potting soil (a triple mix would be perfect),  making sure that a leaf node on the stem is below the soil surface.  Water, and place a clear plastic pop bottle (large size with the bottom cut out) over the pot to act as a greenhouse.  Place the pots (it is best to do several so you will get at least one setting roots) in a bright shaded area.  Rooting should happen in a month, or so. 

Ron ~ zone 6b ~ Ontario