The relationship between the far infrared colour indices and different tracers of the physical properties of the interstellar medium, from left to right: first column: the logarithm of the star formation rate (in M_⊙ yr^-1) measured as described in Boselli et al. (2009); second column: the logarithm of the birthrate parameter b (or the specific star formation rate SSFR); third column: the logarithm of the Hα effective surface brightness (in erg s^-1 kpc^-2); fourth column: the H-band effective surface brightness (in AB mag arcsec^-2);  fifth column: the metallicity index 12 + log (O/H); sixth column: the Balmer extinction A(Hα) (in magnitudes); seventh column: the FUV attenuation A(FUV) (in magnitudes). Red open circles for Sa-Sb, green empty triangles for Sbc-Scd and blue open squares for Sd-Im-BCD. The typical error bar is indicated with a black symbol.