It's the 2 larger ones of the batch that go into dark stages - but they've got the most brightest blue coming through the fins in comparison to the others, is this a stage they undergo when they colour up?? It could be an aging thing because the largest of the 5 has stopped turning dark altogether.
BUT also - could it be because half my tank is bare bottom (for easy cleaning with these smaller Discus) and so they camOuflage to the colour?? They go their normal colour when on the side with the gravel.
Observation made by staring at them for almost half an hour.
The larger ones dOn't pick on these smaller ones, and they're all friendly enough since they eat whiteworms from the tip of my finger so I can't be stressing them out with my presence in the room.