Color–magnitude plots. Top panel: in the direction of JKCS 041; top-middle panel: toward JKCS 041 once the SSW octant has been flagged because contaminated by a nearby structure, see text. Middle-bottom panel: in a control area of the same solid angle as the top panel; bottom panel: toward IRC0218A. Solid lines shows the fitted color-magnitude relations of the two clusters, whereas shading indicates the simpler color range 1.85 < z′ − J < 2.15. Slanted and vertical dashed lines indicate magnitudes where the S/N = 15 in J (vertical) or z′ (diagonal), and therefore delimit the region where catalogs should be complete. JKCS 041 red sequence galaxies are 0.32 mag redder than the red sequence of IRC0218A, at z = 1.62, indicating that JKCS 041 is at z ≫ 1.62.