Table 1: Mean colours of Seyfert galaxies from Clavel et al. (2001) and ULIRGs from Klaas et al. (2001). N gives the number of objects used for deriving the two colours, respectively.
$H - K_{\rm s}$ N $K_{\rm s} - LW2$ N

Sy 1 (<1.8) 0.59 $\pm$ 0.18 25 2.8 $\pm$ 0.6 25

Sy 2 ( $\ge$ 1.8) 0.39 $\pm$ 0.18 23 2.7 $\pm$ 0.8 23

SBs-ULIRGs
0.49 $\pm$ 0.17 21 3.9 $\pm$ 0.5 7

AGN-ULIRGs 0.94 $\pm$ 0.35 5 3.9 $\pm$ 0.4 5

**Table 1:** Mean colours of Seyfert galaxies from Clavel et al. (2001) and ULIRGs from Klaas et al. (2001). N gives the number of objects used for deriving the two colours, respectively.
	$H - K_{\rm s}$	N	$K_{\rm s} - LW2$	N
Sy 1 (<1.8)	0.59 $\pm$ 0.18	25	2.8 $\pm$ 0.6	25
Sy 2 ( $\ge$ 1.8)	0.39 $\pm$ 0.18	23	2.7 $\pm$ 0.8	23
SBs-ULIRGs	0.49 $\pm$ 0.17	21	3.9 $\pm$ 0.5	7
AGN-ULIRGs	0.94 $\pm$ 0.35	5	3.9 $\pm$ 0.4	5

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