The use of colour was desired, but the process remained complex where colour was added onto the black and white images. One of the earliest procedures was hand colouring by large groups of employees painting the film frame by frame, which is a similar industrial process of early animation drawings. Another way was creating an emotional atmosphere to the film by dyeing sequences, which is evident in Robert Weine's German expressionist film Cabinet of Doctor Caligari (1920). In Nosferatu (1922) the colour is used to provide a internal explanation about the characters, which is exemplified by green reflecting Ellen's mental instability. However, the development of sound conflicted with the tinting process because it had a tendency of bleeding onto the audio track.
The additive colour process was introduced, which used red/green filters on a rotating colour wheel in sync with the film. It was projected onto the film removing the issue of bleeding, but the prcoess was highly unstable.
The subtractive process was more successful and predecessor of technicolor where coloured images were produced on the celluloid and projected onto the screen using white light.