I recently acquired a number of mounted species Dendrobiums. The most recent ones arrived 2-days ago.
I noticed that on the Dendrobium heterocarpus, all of the 4 canes have turned yellow, yet the leaves on
top of each cane are green.
I don't really know what happened and why the canes have all turned yellow.

If anyone can assist me with this I would appreciate it.
Thank You.

Perhaps the change in locations was somewhat drastic, coming perhaps from a more shaded environment to a more sunny location?
A picture might help!

Dendrobium heterocarpum, right?

First of all AlanJ, welcome to the Orchid Forums!! We have a fabulous group of people here with years and years of experience. Some are beginners in terms of orchids while some are some of the best growers I have ever met!
ALL are good people!!

But in order to identify and accurately assess what is going on with your Dendrobiums, images are key. If you could get those and give us a little detail about each question, that would help us to help you.
In terms of Dendrobiums, it happens to be one of the largest groups within the Orchidacea. Culture for these 20+ groups can be very different from one group to the next.