My clematis foliage is turning white. Is this a disease or lack of something?

I've never had it happen so I have no idea what it is or what the recommended treatment would be.

How old is the clematis and are all stems showing some white leaves or just a few stems?

Not sure but it could be a nutrient deficiency in the soil, you can try the 1 tbsp. epsom salts in a gallon of water and drench it once a week and see if that greens them up.

Will try that. I thought this was Warsaw NIke, one I planted a couple years ago but when I looked at it closer, I think it is a Jackmani one I thought had died and one stem came back. It is a rather sad looking stem so will be no big lose if it doesn't make it. Thank you both for your help.

Jackmanii were bred to be as tough as nails. its probably not a disease or a soil issue. is it in full sun? are the leaves that are turning white shaded by the upper leaves or by some other type of larger plant off to the side? the lack of direct sunlight will start to have an effect on them. we have a very large Jackmanii where the lower half is shaded by the top half during the height of summer when the sun is directly overhead. they turn yellow, the white. eventually dropping off. the upper leaves are fine however. this may be a factor for you...?