Upper panel: selection boxes for BL+MS stars and RGB stars are superimposed to CMDs representative of the Sgr dIrr galaxy (left panel) and of the fore/background contaminating field (right panel), from the MOSAIC sample. The colour range adopted to select BL+MS stars is −0.30 <V − I< 0.35. Note that the field CMD samples an area that is exactly three time of that sampled by the on target CMD. Lower panel: cumulative radial distribution of the BL+MS (dashed blue line) and RGB (continuous red line) populations in the same range of magnitude.