Cumulative distribution of interstellar reddening in the Euclid ERO region shown in Fig. 1. Two different methods of estimating the reddening are compared. About 70% of the FoV has a modest reddening of less than 1.7 mag in the visible. This reddening value is used in the reddening vectors shown in the colour–magnitude and colour– colour diagrams of the highly reddened region. This work focuses on the σ Orionis cluster, which is located in the low-reddening region of the FoV.