Colour-colour diagrams from J-PAS filters obtained with the GMM method, based on RI values, colour ranges, and expected colour errors. The dwarf stars from spectral libraries – MILES, STELIB, and ELODIE – are represented by crosses and giant stars by squares, both colour-coded according to their T_eff values. The grey curves represent probability density contours across a 2D density plot. The darker the curve is, the higher the density is. The solid lines show the best separation between the two groups according to the SVM solution (see text).