The comparison of relationships between different far infrared colour indices for galaxies coded according to their different physical parameters as in Fig. 4. The solid and dotted lines indicate the expected ratios for a single modified black body with grain emissivity β = 2 and 1.5, respectively. The short solid and dotted lines in the last column show the expected variations when the temperature T changes from 17.5 to 22.5 K for β = 2 (solid line), and from 17.5 K and β = 2 to T = 17.5 K and β = 1.5 (dotted line). The black square is the expected value (shifted on the X-axis for clarity) for a black body of T = 17.5 K and β = 2.