Thanks whmoorejr for your response.
The RGBW controller does indeed show up in Indigo as multiple devices: one for the Composite device and then another four, one for each color/output. These show up and can be selected individually as the 'Device' under 'Action' in the trigger configuration window. So I configured Triggers for the intended setup but it resulted in the secondary switch also switching the light that is controlled by the primary switch. This primary switch is used to control a Hue lamp also through triggers. Also in order for Indigo to receive the switch commands at all I configured the Indigo Z-Wave interface as the 'Responding Device' under all groups of my switch, which for now I presume is the correct way of doing this.
It starts to come back to me that I have tried this previously (quite a while ago when I last attempted anything). What I think happens is that although in the triggers setup the 'Trigger' as well as the 'Action' device can be set to the correct sub-device (secondary switch and Blue output respectively) Indigo doesn't seem to distinguish whether the primary or the secondary switch is activated. In the 'Trigger' set up I have tried two options: 'Device State Changed' and 'Z-Wave Command Received. However both gave the same result that for both primary and secondary switch only the action for the primary are performed.
This leaves me a bit confused
and again in need of bright