Colour-magnitude diagrams M_V vs. (V − I)₀ with all dLHdC stars represented as well as most known EHe stars, some Magellanic RCB stars, and the Galactic RCB stars for which a Gaia eDR3 parallax was reported with S/N > 2 and for which we were able to convincingly measure their maximum brightness in the V and I photometric bands. For all Galactic objects, we used the median geometric distances inferred by Bailer-Jones et al. (2021), and the error bars on the luminosity scale reflect their associated 68% confidence interval. Top: all stars except for the known Galactic RCB stars are represented. Bottom: zoom on the brightest part of the diagram without the EHe stars and with the Galactic RCB stars. An interstellar reddening arrow representing an extinction of 1 mag in V is represented in both figures. The dashed lines, parallel to the extinction arrows, that are each associated with a warm RCB star (Y Mus), two warm dLHdC stars (A980 and B564), and two mild dLHdC stars (C17 and A182), correspond to the reddening over- and under-corrections we consider to have applied after estimating the respective temperatures from the stellar spectra. The locations of the hot RCB stars MACHO 11.8632.2507, DY Cen, and MV Sgr are indicated with an ellipse. The dotted curved indicates the maximum absolute M_V magnitudes recorded for each bin of the (V − I)₀ colour index.