Wikipedia:Rinn's film holders

Rinn's film holders, also called XCP (X-tension C-one P-arallelying), are devices used for endoral radiographs applying the parallel ray technique. They ensure that film will be perpendicular to X-rays. Their colors can be:
 * Yellow for lateral teeth (molars and premolars)
 * Blue for anterior teeth (incisors and canines)
 * Red for bite-wing radiographs
 * Green for "under dam" radiographs, i.e. radiographs shot when the dental dam is still on.