Top-left panel: K_s vs. (J − K_s) CMD for all novae detected in the VVV area. The colour pattern and symbols are the same as used in Fig. 1. Top-right panel: the corresponding (J − H) vs. (H − K_s) colour–colour diagram. Bottom-left: dereddened CMD for all bulge novae, using the reddening maps of Gonzalez et al. (2012) and assuming the Cardelli et al. (1989) extinction law (no disk novae are plotted). Bottom right: CMD using the reddening-free parameters provided by Catelan et al. (2011). The colour of main sequence stars is shown in the (J − H) vs. (H − K_s) CCD in the case of A_Ks = 0 mag (no extinction, solid line) and for A_Ks = 0.243 (the median value of extinction among our targets, shown as a dashed line; adapted from Ducati et al. 2001). The reddening vector associated with an extinction of E(B − V) = 1, based on the relative extinctions of the VISTA filters, and assuming the Cardelli et al. (1989) extinction law, is also shown in the top panels. Four objects are labelled in the plots: Nova Sgr 2001, Nova Sgr 2005b, Nova Sgr 2008, and Nova Sgr 2009b.