V − I versus B − V colour−colour diagram for probable members of γ Vel. Stars with radial velocities higher than 9 km s^-1 from the mean velocity of γ Vel are crossed out. The empirical main-sequence locus relationship from Kenyon & Hartmann (1995) is over-plotted in green, the theoretical main-sequence locus from BT-Settl (Allard et al. 2011) in cyan, the theoretical pre-main sequence locus for an age of 7 Myr from BT-Settl in purple, and finally the locus obtained from Eq. (C.1) in red. All the colour loci plotted as lines have been shifted assuming an extinction of E(B − V) = 0.038 (Jeffries et al. 2009) and E(V − I) /E(B − V) = 1.6 (Rieke & Lebofsky 1985).