H-Ks versus Ks contour diagram, along with the normalised distributions of H-Ks colour and Ks magnitude for both samples. The green lines represent spiral galaxies in isolated environments, and the red lines correspond to elliptical galaxies situated in densely populated areas. The contours represent 5%, 25%, 50% 75%, and 85% of the data for each sample. The resulting D and p values of the KS test are presented.