clematis leaves trouble

Hi, I've got a trouble with a clematis (multiblue): the leaves of clematis turn grey-silver, though the plant looks healthy. I went to my local garden centre, and they never saw this, don't know what it is. They advised to feed the plant with general fertiliser (777), which I am doing and its shape is ok, but the leaves still grey-silver. Below is a picture taken on Monday (with some tulips "remains" on the ground... oops). Last "detail": my location is Lancaster, and the spot is my front garden, facing West. I bought the clematis less than 1 month ago (Wilko).

Hi, I have a similar problem with a clematis named Durandii and have been thinking that it must be mildew.  This clematis is growing in the ground up a trellis on a fence.  I have other clematis but these are in pots and touch wood do not seem to  be effected.  The Durandii  has suffered this problem for about three years and apart from this looks very healthy and flowers well.  Does anyone know what I can do?