Four panels representing the same colour–colour [4.6]−[12] versus [12]−[22] diagram for different WISE source subsamples. See the explanations in the text and within the figures. The [12] magnitude distribution represented inside the top-right panel corresponds to the known RCB stars (linear scale, coloured bins: red for Galactic, blue for LMC, green for SMC) and to the WISE objects selected after cut #0 (grey bins, logarithmic scale). The names and positions of all known and candidate RCB stars that were rejected by the criterion cut #2 are indicated on the top-left panel.