The plot thickens...
I've mentioned this question to quite a few people and most of them have no idea or talk about rear-facing blue formation lights. One or two, though, have recollections that opaque white lights were indeed part of an infrared IFF system.
Nobody knows exactly how it worked and my friend Google is silent on the matter. I couldn't imagine them using an IR light in the unidentified aircraft and making the nightfighter crews wear IR goggles but apparently it did not work this way.
The most credible suggestion so far is that the nightfighter shone an infraded searchlight at the unidentified aircraft. This would be detected by the "resin lamps" which would then light up. These days you can buy systems based on a similar principle for infantry IFF. RV Jones never mentioned any such system but then maybe he was not told about it.
Your question reminds me that Google is very efficient for new stuff but most of the paper in the world is not in any searchable form. WW2 stories also tend to be useless sources for some systems simply because the pilots were never told the truth about the equipment in their aircraft so their memoirs are no help.
So it seems that the Mosquito quite likely had both formation lights and IR resin lights.