The Z − Y vs. Y − J color − color diagram for the HUDF dataset limited at J < 29.2. Big points are observed galaxies, small black points are CB07 models at 0.0 < E(B − V) < 0.3, with small red points those at z > 6.5. The small blue points are the result of our simulations, with synthetic objects inserted in the FITS images and recovered using the same procedure used for the observed catalog. The solid line is the color cut of the A criterion, while the dashed line shows the B criterion (described in Sect. 3). Candidate galaxies at z ~ 7 selected with criterion C are shown in magenta. Vertical arrows are upper limits in the Z band, while the blue circle at Z − Y > 3.6 is the suspected SNa outlined by Oesch et al. (2010a).