a)m(3.4 μm)− m(4.6 μm) vs. m(4.6 μm)−m(12 μm) colour–colour diagram for a sample of emission-line galaxies detected in the three WISE bands 3.4 μm (W1), 4.6 μm (W2), and 12 μm (W3). Galaxies with Hβ equivalent width EW(Hβ) ≥ 50 Å are shown by magenta filled circles while galaxies with EW(Hβ) < 50 Å are shown by cyan open circles. Twenty newly identified galaxies with m(3.4 μm)−m(4.6 μm) ≥ 2 mag are shown by large black filled circles. b) Same as in a) but galaxies with Hβ luminosity L(Hβ) ≥ 3 × 10⁴⁰ erg s^-1 are shown by orange filled circles while galaxies with L(Hβ) < 3 × 10⁴⁰ erg s^-1 are shown by green open circles. c) Same as in a) but galaxies with Hβ luminosity L(Hβ) ≥ 3 × 10⁴⁰ erg s^-1 and with Hβ equivalent width EW(Hβ) ≥ 50 Å are shown by red filled circles while galaxies with L(Hβ) < 3 × 10⁴⁰ erg s^-1 and with EW(Hβ) < 50 Å are shown by blue open circles. For comparison, gray dots in (c) show the location of QSOs selected in the SDSS.