Here is my five foot Hoya Carnosa vine. The leaf color on this 4-year-old plant has been traditional green, as seen in the first photo. This plant was started from a cutting taken from my own large plant.

Recently this plant has started a new leader, half way up the plant, but the leaves are maroon. I realize new leaves sometimes start out dark and develop into the rich, dark green color. I think this is different. You be the judge.

Notice on this junction there are distinct green leaves and maroon leaves, too. All leaves on this cluster emerged and developed at the same time.
Also, this is the only 3" pot that the soil is covered with pebbles.
I have not fertilized in 3 years.
I lightly water once a week.
What could have caused this?