A broken wrist does involve broken wrist bones, twisted nerves and mangled blood vessels. There are four major arteries going from the arm into the hands that are visible and a bundle of nerves that go from the arms through the carpal tunnel to the fingers.
Purple indicates that smaller blood vessels have been broken and are bleeding and the blood is dying. One way to reduce the bleeding is to raise the arm and hand and keep the hand raised at or above the neck level. Gravity should work to reduce blood flow through the wrist. Cold or ice compress may also reduce blood flow through the wrist.