Illustration of the DR method, using the case of IC 4499 in the (V, V − I) CMD plane as an example. Gray dots show the full reference photometric catalog. The manual preselection box is plotted in orange. The sample of stars belonging simultaneously to the four boxes in the (V, B − V), (V, V − I), (V, B − I), and (B − V, V − I) planes is plotted in blue. The median ridge line (MRL) is plotted as a yellow curve, bracketed by its uncertainty curves. The color displacement ΔE(V − I), is computed for each star (red star symbol) along the reddening line (red line), which intersects the MS on the red dot. This is the position that the star would have on the MRL if no reddening or photometric errors were present.