Surface brightness vs. visual extinction in the Draco nebula. The relationships are shown from bottom to top in different colours: 3500 Å (u) (black dots), 3920 Å (magenta, shifted by +20 units), 4030 Å (blue dots, +40 units), 4670 Å (b) (blue dots, +60 units), 5250 Å (black dots, +80 units), and 5800 Å (red dots, +100 units). The crosses at A_V = 0.07 mag indicate the zero level for each surface brightness band. To guide the eye approximate linear fits are shown as dashed lines. Data for positions 1 and 3 (see Table 3) deviate by more than 3σ in most colours and are not shown in this plot.