Oddy, Robert J.Willis, Philip J.2014-10-212014-10-2119911467-8659http://dx.doi.org/10.1111/1467-8659.1020121We propose an intuitively simple way of representing colour which has the additional virtue that, it permits mixing and overlaying of transparent and opaque paints to an arbitrary degree. Our approach is related to the earlier alpha channel model used for compositing. It includes this as a special case but has applications in many other areas, especially animation, paint programs and graphics libraries.10.1111/1467-8659.1020121121-127