Distribution of the photometrically selected non-QSOs in the colour–colour diagram from present VMC data. (Top row) All positionally matched sources. (Middle row) Sources with a slope of variation in the K_s band  > 10^-4 mag/day. (Bottom row) Sources with photometric errors  <0.1 mag and quality flags  = 0 in the Y, J and K_s bands. (Left column) Definite (blue circles) and probable (cyan triangles) background galaxies. (Middle column) YSOs (red circles). (Right column) PNe (green squares), diffuse sources (yellow reversed triangles), evolved stars (magenta circles) and other stars (black triangles). Lines are as in Fig. 2.