Corrected color (g − i)_o vs. stellar mass diagram of optically selected galaxies limited to LTGs (subsample 2). The colors are corrected for extinction in the Milky Way and for internal extinction according to the prescriptions of Appendix A. LTGs undetected by ALFALFA are represented by green symbols. LTGs detected by ALFALFA are given in blue. Red symbols denote the subsample of the ALFALFA-selected galaxies that were followed-up in Hα3.