Top panel: mass-to-light ratio M_⋆/L_i as a function of the rest-frame colour g − i for the 63737 ALHAMBRA star-forming galaxies with F814W ≤ 23 at z < 1.5. The solid lines show level contours in the density of galaxies as in Fig. 2. The grey scale shows the median fitting model to the data, . The blue area represents the derived MLCR, log₁₀ (M_⋆/L_i)=1.411 + 0.212(g − i)+0.144(g − i)², and its 1σ intrinsic dispersion, σ_SF = 0.06. Side panels: normalised projected histogram in g − i (upper panel) and log₁₀ (M_⋆/L_i) (right panel). In both panels the observed distribution is presented in filled blue, and the derived median model in solid black. Bottom panel: comparison between the observed ALHAMBRA mass-to-light ratio and that expected from our median relation (blue filled histogram). The blue solid line is the best Gaussian fit with median ⟨ΔΥ⟩ = − 0.01 and σ_ΔΥ = 0.09. The black solid line illustrates the estimated intrinsic dispersion unaffected by observational uncertainties.