Run Wild, Run Free - Richard C. Sarafian

Philip Ransome, a northern English boy about 10 years old, has been mute since age 3 and spends his days roaming the moors alone. His parents despair of a cure. One day he sees a singular wild albino pony with blue eyes and befriends it avidly. A kindly retired colonel who accepts Philip as he is, a girl his age, and a pet falcon she gives him provide him with more things to love and care about. Gradually Philip emerges from his shell. But the way out is full of heartbreak and setbacks.