Aphids...
Next, it appears to be Nitrogen starved - Bougain has a very low N rating of 8... In Spring when ours go back out after a long Winter they go into a shaded area for a few weeks, get 20-20-20 to inspire vegetative growth which is normally deeper green.
They are also potted in organic, but very fast draining, almost all sphagnum peat, stays damp but drains and allows air. The peat sounds counter productive but it drains so well the acidity does not bother them at all.
When they are darker and full here we put them out in full sun 6 plus hours a day, stop fert, and let them whither a bit the first week. Followed by flooding daily they do lighten up a bit but start to bloom a lot. Bougain is designed for Bloom and we find just controlling a 20-20-20 works just as good.
Being an outdoor/indoor plant up North they do require a bit of bouncing around but they also need to be potted here so it all works out
Grimmy