Colour−colour diagram: PACS/PACS diagram: F₇₀/F₁₀₀ versus F₁₀₀/F₁₆₀. Top: the colour and symbol code differentiates DGS (purple crosses) and KINGFISH galaxies (orange downward triangles). Bottom: the colour code delineates the different metallicity bins this time. Crosses and downward triangles are still representing DGS and KINGFISH galaxies, respectively. For both plots, the curves give theoretical Herschel flux ratios for simulated modified black bodies for β_theo = 0.0 to 2.5 and T from 0 to 40 K in 2 K bins and from 40 to 100 K in 10 K bins, as black dots, increasing in T from left to right. Lines of constant T are indicated as dotted lines, and a few temperatures have been marked on the plots.