|On an X-ray result picture, why is the film in the background blue? Is this the only way it will show up? If so why?
The X-ray image itself is formed by tiny black silver particles, just as in a normal black and white photographic negative. If those particles were supported by a clear plastic sheet, then the X-ray should appear either clear or black and have no color. The blue you are referring to must be caused either by a colored pigment in the plastic X-ray film sheet or by a colored light used to illuminate the X-ray. I suspect the later. Fluorescent lamps tend to be bluish and the ones used to view X-rays are probably particular blue. It probably increases the apparent contrast in the image so that small variations in density become visible.