NUV− u versus g − i for all radio sources in XXL-S that possess a spectrum with continuum S∕N > 3. The colours have not been corrected for dust extinction. The red squares represent the galaxies classified as early-type absorption galaxies (ETAGs) according to their spectra and the black points represent all the galaxies that were not classified as ETAGs according to their spectra. The ETAGs tend to be found in the colour space defined by NUV −u > 2.0 and g −i < 1.2.