(U − B) vs. (V − K) colour–colour plots for a variety of absolute magnitude ranges. Panels a, b, c, f, g, and h: six colour–colour plots, with data from the isochrone grid. Panel d: colour scheme used in all panels, with different colours representing different ages, and the brightness of the colour representing the metallicity. Panel e: various slices in absolute magnitude used in the outer panels (arrows indicate which slice is shown in which panel), along with six isochrones plotted for demonstration. These isochrones have ages of 2 (green), 5 (blue) and 10 (red) Gyr, and both [Fe/H] = 0.0 (bright) and [Fe/H] = −0.25 (faint).