Forge Filter

Filters are a Forge object in Halo 3 first introduced in the Legendary Map Pack.

Gameplay
The Forge Filter when in game is not visible, however its effects are completely visible, switching a forge filter to Colorblind for example will make the match completely black and white.

Background
The primary function of the Filters is to change, the way maps look like by using special effects. The effects were made to make the Custom Game and Forge experience more enjoyable and different. Once a forge filter is placed it can be set to one of six different effects or tones.

Colorblind
Colorblind applies an effect to the map so it only uses black and white. This for this very reason doesn't use any other colors except shades of gray, white, & black, therefore obtaining the name Colorblind.

Gloomy
Gloomy makes the screen darker, and it outlines objects. The effect like the name describes it, tries to set a gloomy mood. This one might be used mostly by Machinima Producers, for their machinimas. In the Legendary ViDoc, on of the Bungie artists calls it "The Gears of War one", referring to Epic Games' dark and atmospheric shooter.

Juicy
Juicy applies a dark, and richer look to the game. Making the colors seem more rich, and not faded. This effect pretty much eliminates glare, which can give objects and even characters a sort of faded look.

Nova
Nova applies an effect to the map making things outlined at close range, and less detailed and blurred at long range. This effect is almost like a snow blizzard's effect on the eyes.

Old Timey
Old Timey applies a sepia effect to the map. This makes the map look older, another possible advantages for a machinima producer, for producing their machinimas.

Pen & Ink
Pen & Ink applies an effect to the map making it look almost drawn, the map's colors are all reduced to a black and white scheme.

Other Links
Forge

Legendary Map Pack