Colour–magnitude diagram for galaxies along JKCS 041 line of sight (i.e. JKCS 041 and residual background galaxies) within 2 × r₂₀₀. The black dotted lines represent the S/N ~ 5 completeness. The green thick solid line represents the mass cut (M = 1.34 × 10¹¹ M_⊙). The dashed line indicates the blue/red threshold. For illustrative purposes, the light blue dash-dotted line represents the locus of galaxies with a mass in stars at the redshift of JKCS 041 of M_zobs = 0.75 × 10¹¹ M_⊙.