Distributions of the H-Ks colours for elliptical galaxies (left panel) and spiral galaxies (right panels) in an environment classified as isolated (E = 0) and high density (E = 4) in the 14 < K s < 15.5 magnitude range. The vertical lines represent the mean H − K s colour, and the error is indicated by the grey shadow area, as measured for the five galaxies that were spectroscopically confirmed and are part of a galaxy structure, as reported by Galdeano et al. (2023).