Colour–colour [3.4]−[4.6] versus [12]−[22] diagrams. Top-left: distribution of all selected WISE targets of interest that have a valid measurement in all four WISE bands. The diagram is colour-coded with the J − K colour index. Two groups of objects are emerging; we are separating them pragmatically into two zones, A and B (see text for more details). Top-right: same sample of objects is represented in grey, while all known and candidate RCB stars are overlaid with large dots. Most RCB stars are located in zone A. Bottom-left: same diagram as the preceding except that the RCB SED models are added, colour coded with their shell temperatures. Bottom-right: here all known RCB stars are represented again by large red dots, while the large squares represent all the targets of interest that have already been followed-up spectroscopically. They are colour-coded respective to their spectral classifications.