premature Coloring of the leaves (red, purple, grayish) sometimes indicates a phosphorus deficiency. You creepers may have grown so much as to use up all the available nutrients. Without soil and tissue testing it is hard to say. You can always try about 1/3 cup of 10-20-10 with lots of water.

Perhaps you have a leafhopper problem.

I have grown Virginia Creeper for 25 yrs and it often has a problem with these little beasties. The leaves on the ends of my longest vines are very prematurely red this year. I have assumed it is due to the incredible leafhopper infestion I had last year, and to a much lesser extent this year.

They hang out on the underside of the leaves, are small, pale green and hop. They suck the juices out of the leaves, causing them to die.

If the infestation is really bad you can hear and see them when you walk by, as they panic at your intrusion.

You can get biological controls for them, but timing of the application is important, as is doing the right thing to keep them around.