g − r versus r − i colour–colour diagram. Colours of the cirrus derived in the West filament are in black. The integrated colours of the group members in HCG 86 are in blue. The average value of the IGL in the group is shown as magenta triangle (see Sect. 4.1). The small red points are the colours derived for Cirrus from Román et al. (2020). The two vertical dashed lines indicate the range of g − r colours of the IGL in the HCGs studied by Da Rocha & Mendes de Oliveira (2005), Da Rocha et al. (2008). In this colour–colour plot the region in which the IGL lies is different both from those typical of cirrus (Román et al. 2020) and from cirrus in the HCG 86 space. This confirms that IGL in HCG 86 are not largely contaminated by cirrus.