1. A method of populating cells in a look-up table (LUT) which maps from color values in a source color space to corresponding color values in a destination color space, wherein the LUT includes cells corresponding to color values within a spectrum locus and color values outside the spectrum locus, wherein the method comprises: for cells within the spectrum locus, calculating color values in the destination color space using a color transform, wherein the color transform is constructed based on device profiles for the source and for the destination, and populating corresponding cells of the LUT based on the calculated color value; training an artificial neural network using the calculated color value; and for cells outside the spectrum locus, populating corresponding cells based on outputs of the trained neural network.