Brief Answer:
There are 2 reasons for you pale skin.

Detailed Answer:
Hello! Thank you for your question on HCM! Regarding your concern I would explain in simple words the reasons of your pale skin during exercise:
There are 2 main reasons why it goes pale:
1) anemia (low hemoglobin level is reflected in the pale skin especially during physical exertion), seems that you fulfill this criteria. The scale of its contribution depends on the level of hemoglobin.
2) redistribution of blood supply in physical and mental stress conditions reflected with a lowered blood flow to the skin and greater blood supply to vital and visceral organs (such as brain, heart, liver, kidneys, etc). This blood redistribution occurs more often when the cardiac output is inappropriate, and increases not proportional to all body demands. In your situation your cardiac ultrasound shows mitral regurgitation (and another regurgitation), also Ebstein anomaly. All this echo - detected disorders make the heart work less efficiently and produce suboptimal cardiac output during exercise.

So, these are the two main mechanisms explaining your pale skin.
Hope to have been helpful, and to have fulfilled your expectations.
Feel free to ask me whenever you need.
Greetings from Dr. Iliri

---