Observed (u − r) colour as a function of morphological parameters. From left to right: Sérsic index, n_I, concentration index, c_90/50, and wavelength-dependent ratio of Sérsic indices . Triangles and solid lines in gray (histograms) show LT, squares and dashed lines in black (histograms) show ET galaxies. The top histograms correspond to the respective value, as indicated in x-axis label, while right-hand histogram show the (u − r) colour distribution. All histograms represent density distributions. Horizontal dot-dashed line in black shows (u − r) = 2.5. Red dashed line show linear discriminant analysis result from de Diego et al. (2020). Dashed lines in magenta represent limits from Vika et al. (2015): vertical cut in (u − r) = 2.3, while on the left and right panels horizontal dashed-lines in magenta represent log(n_I) = 0.4 and , respectively (see Sect. 6).