Selection of RC locus (black points) and its colour spread (orange points) from the 2MASS colour-magnitude diagram (J − K_s, J; central panel) for 1° ×1° field centred at ℓ = 45° and b = 5°. The figures labelled 1–10 represent J − K_s density histograms of the corresponding J-magnitude bins. A detailed discussion is presented in the text. The black dots in the central plot show the last 100 points in the lowest-density region.