Q. My climbing rose has deformed red stem growth and discolored flowers
The most common reason for a change in flower color is canes coming from below the root graft. You mentioned the rapid growth of new canes but are these discolored roses growing on canes that have sprung from the base of the plant or new growth on the same canes that bore roses earlier in the season?
There is also a virus that produces excessive, dense, red growth on roses that can be thornier, thicker and breaks off easily. If the stems have an extra thorny, soft look, they may have rose rosette disease or witches broom of rose. The virus is spread by mite and the primary symptom is this distorted, soft, red growth.
Here is a link to information from the American Rose Society about the disease as well as an FAQ from Clemson and an article from the University of Tennessee about it. You will need to take a close look at your rose and its symptoms to see how they compare to the information. The outlook for your rose, if you agree this is what you have, is bleak and you will want to act quickly to protect your other roses.
Courtesy of NYBG Plant Information Service