Relative variations of the mean extinction curve δ(A_λ/A_V)|_n (solid line) at a given gas density (color-coded as indicated in the panel) with respect to the galactic extinction curve in the G10LG simulation at t = 400 Myr. The dashed lines indicate the 1-σ scatter for each sampled density. The error bars stand for the scatter of the observed extinction curves of the Milky Way from Fitzpatrick & Massa (2007) relative to the mean extinction curve from Pei (1992).