The grey points represent the colours of 10 000 objects in field 1 of the CFHTLS Deep. The black boxes are defined by Eqs. (1)–(3) and are used to select u-(top panels), g-(middle panels), and r-(bottom panels) dropouts. The coloured tracks represent the colours of a template galaxy as a function of z. They are evaluated at intervals of Δz = 0.1. The symbols mark redshifts from 2.5 to 3.5, from 3.2 to 4.2 and from 4.2 to 5.2 for u-, g-, and r-dropouts respectively. The green curve with  × -symbols represents a reference model, a 100 Myr old continuously star-forming template with a dust attenuation of E(B − V) = 0.25. In the left panels we consider redder (bluer) templates by increasing (decreasing) the template age, see the red (blue) curves and the  △  (◇)-symbols. In the right panels we consider redder (bluer) templates by increasing (decreasing) the amount of dust in the template, see the red (blue) curves and the  △  (◇)-symbols. Note that we use a distribution of dust in our fiducial analysis (see Sect. 3.1).