Observed UV slope β as a function of the V-band (left) and FUV (right) attenuation (black), assuming the relation between the attenuation curve slope δ and the attenuation shown in Fig. 7. For comparison the evolution of β for starburst and SMC-like attenuation curves are shown in red and blue, respectively. We see that the evolution of β with the attenuation follows a very different track compared to the starburst and SMC curves. The consequence is that, in the case of main-sequence galaxies at z ∼ 5, β cannot easily be used to infer the attenuation of galaxies