Can you add a photos? What is your soil like as far as texture and pH? Has your weather been unusual in any way? How long have they been in the ground? I think that the yellow leaves with green veins might imply a nutrient issue, but I'd like additional info.

Don't know how to do pics. Soil is good, PH high, but I add additional iron. Weather-1 -17 day this winter. Temps up and down, still using furnace here at nite. All other clems are doing well, color good in leaves and lots blooming. Rebecca didn't show yet. Both JS and VV been in ground over 5 years. Like I say VV has white in leaves, looks like virus, do clems get mosiac?

To post a photo, take a photo and load into your computer in a folder you can easily find. Then click in the box used to do a followup posting at the bottom of this thread and click on the Photo icon below. In the box that pops up, navigate to where your photo is on your computer, click on the photo and wait until it appears in the followup box. Then either repeat the process to add another photo or click submit if you have uploaded all you want. I find it really difficult to do diagnosis from a description.

Or take it to a master gardener workshop or your cooperative extension or do a web search for clematis mosaic virus. Be thoughtful in what you use of what pops up in a web search - I usually use university or botanic garden websites for accurate info.

I thought pH might be high in your area, and if you are on the edge of what clematis are comfortable with as far as pH, JS's yellow leaves and green veins sound like a nutrient issue that might be caused if it is a bit more sensitive to pH than other clems or if there is slight variation in the pH and organic matter in different parts of the garden. It doesn't mean the nutrients aren't there, but the high pH sometimes makes them difficult for the plant to access.