has consistent FIR colours to the main correlation or the subcorrelation (Fig. \[fig:clrdat\]). This implies that the wavelength dependence of the FIR emissivity is not different among the BCDs, the LMC, the SMC, and the Milky Way. In the following section, we examine if the FIR colours of BCDs can really be reproduced with the emission properties adopted by HHS07, who explained the FIR colours of the Milky Way, the LMC, and the SMC (Section \[sec:model\]).

Results {#sec:result}
=======

Interstellar radiation field {#subsec:dep_isrf}
----------------------------

We present the dependence of FIR colours on ISRF. Here we adopt $A_V=0$ [(i.e. the optically thin extreme for the ISRF; Section \[subsec:colour\])]{} to concentrate only on the effects of ISRF intensity. In Fig. \[fig:clr\_Av0\], we show the FIR colour–colour relation ($(60/100)_\mathrm{cl}$ and $(140/100)_\mathrm{cl}$) calculated for silicate and graphite. We observe that the FIR colours of the BCD sample can be reproduced with $\chi\sim 30$–300 except for the lowest data point (II Zw 71). This is consistent with the conclusion in H08 that the ISRF (especially the UV ISRF, which contributes most to the dust heating) in BCDs can be 100 times higher than the Galactic ISRF in the solar neighbourhood.

![Far-infrared colour–colour relations for silicate 