Several color filters used for photography.
color filter definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
colored glass, dyed gelatin, etc., used to produce certain color or light effects, as in photography
color filter definition by American Heritage Dictionary
A photographic filter made of colored glass that modifies the light striking the film by selectively absorbing colors. It is used when taking photographs through haze.