Effect of dust attenuation on the relation between M_HI/M_* and NUV − r colour. The distribution of the Hα-to-Hβ ratio of the α.100_spec sample is shown in the top-left panel. The dashed green lines indicate the division of the sample into three sub-samples. In the other panels, the three sub-samples are shown as green dots in the M_HI/M_* vs. NUV − r diagram. Similar to the middle panel in Fig. 5, the black-and-white contours represent the final ALFALFA 100% catalogue (α.100), while the solid red line is the relation described in Eq. (4). As can be seen, galaxies of different dust contents are shifted along the derived relation, not displaced away from it.