Relation between observed (u−r) and μ_u for the sample of 7 934 galaxies divided into 14 A_FUV bins. Each panel represents consecutive A_FUV bins (Fig. 4 and Table 2). The resulting slope and intercept of the fit are provided within each corresponding panel. The deviation of the (u−r) colour from the linear fit (Δ_ur) and the variability of A_FUV within the range of ±1σ from the linear fit (σ_AFUV) are both indicated in each panel.