The blue-colored tilapia you see here are females with mouths full of eggs/fry. The mums should spit out the fry in a couple of weeks.
If I had panned around, you'd have seen some algae building up on the pvc and walls (you can actually see a little bit of green on the pvc in the vid). The only reason there's any algae to see is because the females have stopped feeding while they brood. Before they started brooding, the tilapia kept the pvc bone-white and the water sparkling (they LOVE algae, consuming it both by filtering the water and by nibbling on underwater surfaces on which it grows).
The males are significantly longer and are white with blue dorsal fins. This was surprising to me, since males of most animal species are usually the showy/colorful sex and the females are usually duller and less colored. Regardless, these white males constantly defend their nests (clean swept patches on the bottom) and try to attract romance (darting up to the school of females and 'flashing' in an attempt to get a lady to follow). You can see one of them flash near the top of the screen at the 20-second mark in the video below, and another at the 34-second mark.
Most of these tilapia are probably 7-9" long right now. They were only 1" long when they arrived about 3 months ago (June 2nd).
