This is a quote from one of my heroes, Andrei Tarkovsky, on colour cinema.
When we watch something going on we don't notice colour. A black-and-white film immediately creates the impression that your attention is concentrated on what is most important. On the screen colour imposes itself on you, whereas in real life that only happens at odd moments, so it's not right for the audience to be constantly aware of colour. Isolated details can be in colour if that is what corresponds to the state of the character on the screen. In real life the line that separates unawareness of colour from the moment when you start to notice it is quite imperceptible. Our unbroken, evenly paced flow of attention will suddenly be concentrated on some specific detail. A similar effect is achieved in a film when coloured shots are inserted into black-and-white.
Colour film as a concept uses the aesthetic principles of painting, or colour photography. As soon as you have a coloured picture in the frame it becomes a moving painting. It's all too beautiful, and unlike life. What you see in cinema is a coloured, painted plane, a composition on a plane. In a black-and-white film there is no feeling of something extraneous going on, the audience can watch the film without being distracted from the action by colour. From the moment it was born, cinema has been developing not according to its vocation, but according to purely commercial ideas. That started when they began making endless film versions of classics.