A color wheel or other switch for changing a projected hue

Hue

Hue is one of the main properties of a color, defined technically , as "the degree to which a stimulus can be describedas similar to or different from stimuli that are described as red, green, blue, and yellow,"...

 (e.g., for an optical display) is a device that uses different optics filter

Filter (optics)

Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....

s within a light beam

Light beam

A light beam or beam of light is a narrow projection of light energy radiating from a source into a beam. Sunlight is a natural example of a light beam when filtered through various mediums...

. Common usage includes continuously-rotating wheels for seasonal home displays (e.g., at Christmas

Christmas

Christmas or Christmas Day is an annual holiday generally celebrated on December 25 by billions of people around the world. It is a Christian feast that commemorates the birth of Jesus Christ, liturgically closing the Advent season and initiating the season of Christmastide, which lasts twelve days...

) and controllable color wheels for a particular instrument (e.g., SeaChanger Color Engine

SeaChanger Color Engine

The SeaChanger Color Engine is an electro-mechanical device that is used to control light color in entertainment-industry lighting applications. The unit employs four overlapped color filter wheels, inserted into a light beam near its source, to produce colored light. This is in contrast to color...

 for stage lighting

Stage lighting

Modern stage lighting is a flexible tool in the production of theatre, dance, opera and other performance arts. Several different types of stage lighting instruments are used in the pursuit of the various principles or goals of lighting. Stage lighting has grown considerably in recent years...

), while non-wheel devices include scrollers and semaphore types with lever arms (e.g., on the 1897-1917 Grand Army Plaza fountain).