Ratio R_W of the shorter two and longer two wavelength bands of WISE plotted against XUV. Blue crosses are objects without significant emission lines in the spectrum (spectral type 0 and 1), green open squares LEGs (spectral type 2) and red dots are HEGs (spectral type 3 and 4, see Table 4). The dashed horizontal line is the expected R_W for elliptical galaxies with only an old stellar population. The magenta line is the linear regression of R_W against XUV (see text).