Colour Effect Filters
Colour effect filters are used to produce special effects on colour film. Perhaps the best-known of these are the graduated filters, clear at the bottom and gradually changing to a colour, often used to colour skies.
They do more than just colour the sky, because the coloured portion of the filters also helps to block some of the light in brighter areas, helping to prevent over-exposure of the sky. Filters of this type are normally supplied in rotating mounts, so that the filters can be positioned exactly as required.