Running mean of the average (g − i) colour profiles of the ETGs in Fornax, in three different mass bins: 8.9 ≤ log M_*/M_⊙ ≤ 10.5 (blue), 10.5 ≤ log M_*/M_⊙ ≤ 10.8 (green), and 10.8 ≤ log M_*/M_⊙ ≤ 11.2 (magenta). Blue dashed line indicates galaxies in the low-density region, while the blue continuous line indicates those in the high-density region of the cluster. The dashed and the continuous vertical arrows denote the position of the average transition radii, R_tr1 and R_tr2 respectively, in each mass bin. The dotted lines represent the fits to the colour gradients between transition radii.