We use filters in cinematography to alter the image either for technical reasons to correct the colour of the light to that required by the film we are using, or because we may wish to change the image in some way that will enhance our storytelling powers. The former is often necessary, the latter much more fun.
The majority of coloured filters are known by numbers or a combination of numbers and letters – for instance, 85 and 85B. These are simply the catalogue number they are to be found under in the Eastman Kodak Wratten Filter Catalogue. All filter manufacturers will use the Wratten filter numbers for their version of the filter in their list that conforms to the transmission characteristics of the filter in the Wratten ...