Illustration of two steps of the first method. Left panels: i − z colour histograms in two fields-of-view (candidate 13 and candidate 8) where the default background (pink line) is either too high or too low. The adjusted background is overplotted in green. Middle panels: resulting colour distribution is the background is left unadjusted. For comparison purposes, the Gaussian models of the red sequence and the blue cloud are shown in pink and blue, respectively; although, they were computed with an adjusted background. The mauve dash-dotted line is the “boundary” used in method 2, 3, and 4. Right panels: colour distribution once the background was adjusted.