Now it's getting interesting, jaj.
If you're suddenly finding variegated leaves, it could be a virus, or it could be the result of herbicide contact. But it could also be a "sport".
What you need to do now is try to propagate from the variegated part of the plant. Unfortunately, clematis are tricky.
You can try soft cuttings (tip growth with two or three nodes - leaf joints - but you'll need hormone rooting powder). The chances of success are slim.
Clematis are best propagated by layering, ie pinning a new growth to the ground, and let nature take it's course. That's how the parent species spreads naturally.
Good luck, and remember protocol forbids you from naming a new plant after yourself