Q.Minature Climbing Rose Has White Leaves. What Can Cause This?
This plant has been doing well up to a few weeks ago.

White leaves sounds like a bad case of Powdery Mildew. Powdery Mildew is a fungus that attacks rosebushes foliage and new bloom buds at times. The very best fungicide I have found to knock it down and get rid of it is called Green Cure. Green Cure comes in a white powder form in a plastic container. There is a measuring scoop/spoon in the container. Add two scoops/spoonfuls of the green cure powder to each gallon of water in a sprayer. Shake it up well, then spray all the foliage down well with the product. Follow up in 5 to 7 days with another spraying. Use the same timing until the powdery mildew is gone. Green Cure is available for purchase at Amazon.com. Here is more information on it for you: http://www.greencure.net/
Here is a link to an article I wrote on various diseases roses can get and how to deal with them for you as well: https://www.gardeningknowhow.com/ornamental/flowers/roses/rose-bush-diseases.htm