Position of GRGs and giant radio quasars (GRQs) (733 sources from GRG catalogue) in the mid-IR colour–colour plot using WISE mid-IR magnitudes (W1, W2, W3, and W4 have 3.4, 4.6, 12, and 22 μm Vega magnitudes, respectively). Objects from the GRG catalogue are included. Region I: [W1] − [W2] ≥ 0.5 and [W2] − [W3] < 5.1 is mostly occupied by HERGs and quasars. Region II: objects that have [W1] − [W2] < 0.5 and 0 < [W2] − [W3] < 1.6 are basically LERGs. Region III: star-forming galaxies and LERGs lie mostly in this region ([W1] − [W2] < 0.5 and 1.6 ≤ [W2] − [W3] < 3.4). Region IV: ULIRGs lie in the region of [W1] − [W2] < 0.5 and [W2] − [W3] ≥ 3.4. All the sources have z < 1. The triangle in the plot and the U in the legend indicate the upper limits of the W3 magnitudes.