and graphite (asterisks and open diamonds, respectively). The different points correspond to $\chi =1$, 3, 10, 30, 100, and 300 from high to low \[140/100\]. [We adopt $A_V=0$ (optically thin extreme) for the ISRF.]{} The same data as shown in Fig. \[fig:clrdat\] as well the the main correlation and subcorrelation (dashed and dotted lines, respectively) are also presented. \[fig:clr\_Av0\]](clr_Av0.eps){width="8.5cm"}

Our results not only confirm the warm *IRAS* (*Infrared Astronomical Satellite*) 60 $\mu$m–100 $\mu$m colours of BCDs [@hoffman89], but also show high temperatures of dust contributing to the emission at $\lambda >100~\mu$m. A few Virgo Cluster BCDs observed by *ISO* (*Infrared Space Observatory*) show relatively cold 170 $\mu$m–100 $\mu$m colours [@popescu02], indicating that the presence of warm dust is not necessarily the case at least in cluster environments.

We also find that the calculated FIR colours cover the area between the main correlation and the subcorrelation. With $\chi\la 10$, the colours trace the main correlation, which is appropriate for the Milky Way, the LMC and the SMC. On the other hand, the FIR colours are rather similar to the subcorrelation for $\chi\ga 100$. While @hibi06 and HHS07 claimed that the subcorrelation can be reproduced with dust emission with multiple temperature components, 