Late Season Harvest

Yesterday, my husband and I went hiking for a very specific harvest: red colored blackberry leaves. This coloration naturally occurs late in the Fall and in the Winter when the plant goes into its dormant state.
We have lots of Himalayan Blackberries around here (a non native species that some consider to be an invasive weed). They are easy to recognize with their purplish stems. The back of the leaves is white with purple thorns. When they're fruiting, the fruits can get pretty big, sweet and juicy...They're also very productive!
So not only did we find the red leaves but we also found a few last juicy fruits, right under a cluster of Elder Trees (I call them the Three Sisters). Brambles and Elders seem to like each other's company ;).
So why harvest red blackberry leaves?
In "Drink in the Wild" by Hilary Stewart, it is said:
"...Leaves for tea are at their best when they are old and turning red. Dried leaves remaining on the plant in winter are also good for tea."
I don't know yet how the change in color is going to affect the taste of the tea. I also wonder if the red pigmentation implies a beneficial effect on blood circulation and strengthening the capillaries. It's supposed to be one of Blackberry's healing gifts...