Comparison between the UGR (left panel) and UGY criteria (right panel). Different colours and shapes mark the position of galaxy models. Cyan points mark the LBGs in the redshift range 2.7 <  z <  3.3 with Z/Z_⊙ = 0.2 − 1.0, age = 0.01, 0.1, 0.3, 0.5, 1, 2 Gyr, constant SFR, at an increasing extinction E(B − V) = 0 − 1.0 at 0.05 intervals; black filled squares indicate LBGs out of the desired redshift range; red crosses indicate red passively evolving galaxies at lower redshifts, with Z/Z_⊙ = 0.2 − 1.0, age = 1 − 13 Gyr, τ = 0.1, 0.3, 0.6 at an increasing extinction E(B − V) = 0 − 0.2 at 0.05 intervals; green open circles mark low-redshift dusty star-forming galaxies with Z/Z_⊙ = 0.2 − 1.0, age = 0.01 − 1 Gyr, constant SFH at an increasing extinction E(B − V) = 0.5 − 1.5 at 0.1 intervals; stars from the Pickles (1985) library are shown as blue filled triangles. The magenta continuous lines indicate the LBG selection windows.