Traditionally, non-linear diffusion processes and watershed segmentation have been well studied for greyscale image segmentation. In this paper we extend their use to colour images. First, we formulate a general definition for a non-linear diffusion process using the concept of an activity image that can be calculated for several image components. Then, we explain how the cleaned activity image is fed through a watershed algorithm yielding the colour image segmentation. Finally, the qualitative performance is illustrated with results for real colour images.