Colour–colour (J − H)₀ vs. (H − K)₀ diagram with 2MASS magnitudes corrected for extinction, showing the positions of all known and new Galactic HdC and EHe stars, represented with colour points, in comparison to giant stars (M_G ≤ 0 mag, BP − RP > 0.5 mag, G < 15 mag) selected in Gaia eDR3 (groups A and B). Left: distribution of all giant stars with an interstellar reddening E(B − V) lower than 0.5 mag. Right: zoom on the lower left corner. The distribution of giant stars impacted by interstellar reddening between 0.5 < E(B − V)≤1.0 mag is indicated in red, and the distribution of the ones of lower reddening is shown in blue. The selection area is delimited with red lines. The interstellar dust reddening vector is represented for an extinction A_V of 1 mag.