Dr. Rikenstein's Notes: Page 215

This photo was taken shortly after the accident that fundamentally changed William Rumble forever. As you can clearly see, the atomic power within him has caused his skeletal structure to glow a vivid green color. Although further testing is required, it appears that the glow becomes more pronounced as he uses the energy burning within him. When fully "powered up" for lack of a better term, his skeleton glows to the point that it is visible beneath the skin.
This condition is not present at all times, and as long as young William chooses to remain calm and not take advantage of his newly acquired "abilities" he passes as completely normal, if somewhat on the juvenile delinquent side.
This requires further study for the sake of Science and the American Way.