Distribution of the inner g − r (left), g − i (middle), and r − i (right) colour gradients as a function of the surface brightness profiles of the galaxies represented as box plots. The boxes extend from the lower to upper quartile values of the gradient distributions with a red line at the median. The whiskers extend from the box to show the range of the data. Outlier points are those past the end of the whiskers and are represented with crosses. We also show the histograms for each distribution colour coded according to the SB type: type I (green), type II (blue), and type III (red). Dots with transparency represent all the observational values. The median values of all the distributions are linked using a blue line to highlight the tendency.