**Table 9:** Comparison of average values of colour gradients for the subsample IR₀ of objects with zero IRAS 100 $\mu$ flux and the subsample IR₁ of objects with non zero flux (Knapp et al. 1989).
Y	IR₀	N	Av₀	IR₁	N
$\Delta _{BV}$	IR₀	17	$-0.065\pm.005$	IR₁	35	$-0.067\pm.004$
$\Delta _{UB}$	id	13	$-0.166\pm.015$	id	27	$-0.152\pm.007$
$\Delta_{BR}$	id	14	$-0.083\pm.008$	id	28	$-0.081\pm.005$
$\Delta_{VI}$	id	15	$-0.057\pm.009$	id	34	$-0.063\pm.006$
$\Delta _{VJ}$	id	17	$-0.106\pm.026$	id	35	$-0.147\pm.015$
id	id	16	$-0.089\pm.014$	id	34	$-0.139\pm.013$
$\Delta _{VK}$	id	17	$-0.199\pm.029$	id	35	$-0.237\pm.018$
id	id	16	$-0.175\pm.017$	id	34	$-0.227\pm.015$
$\Delta_{JK}$	id	17	$-0.090\pm.009$	id	35	$-0.092\pm.005$

1) Gradient Y; (2) subsample IR₀; (3) N number of objects; (4) average Av₀; (5) subsample IR₁; (6) N number of objects; (7) average Av₁. NB: the 2nd. line for $\Delta _{VJ}$ , $\Delta _{VK}$ gives the solution after the rejection at $3\sigma$ of NGC 4660 from the subsample IR₀ and 5866 from IR₁.

Source LaTeX | All tables | In the text

	1 Introduction
	2 Collecting the gradients
	3 Properties of colour gradients
	4 Simulated datasets of colour gradients
	5 Concluding summary
	References