Colour–M_* diagram. Blue points show Hβ ELS and green contours represent the whole OTELO sample. The filled contour in grey shows the envelope of SDSS-DR7 data, while filled red and blue contours show red and blue clouds separated with the empirically estimated limit of Bluck et al. (2014). For the Hβ sample, we differentiate the robust sub-sample of 27 galaxies from the remaining 13 with blue circles and black squares, respectively.