1. Apparatus for processing image data, comprising storage means arranged to store instructions, memory means for storing said instructions during execution and for storing image data, processing means for performing image processing in which said image data is processed to modify color values, and display means for facilitating user interaction with said image processing, wherein said processing means is configured such that, in response to said instructions, said image data is processed by steps of: identifying a source color; identifying a destination color; identifying three fixed points in color space; identifying a source color volume defined by said source color with said three fixed points; identifying a destination color volume defined by said destination color and said three fixed points; and defining a correspondence transformation between said source and destination color volumes; and applying said correspondence transformation to said image data.