Dependence of the temperature of the cold clumps and the dust emissivity spectral index β on the colours at low and high frequency around 857GHz. The temperature is obtained by performing an SED fit with a fixed β = 2 (upper panels) and a variable β (middle panels), while the associated β is shown in the bottom panels. All quantities are given as a function of the S₃₀₀₀/S₈₅₇ colour (left column) and of the S₃₅₃/S₈₅₇ colour (right column).