Have you checked your water parameters?

One way I used to get my Discus, distant cousins of Angelfish, to breed was to first feed them heavily with live food like black worms or frozen bloodworms, cleaning up anything that was not eaten. After a a week of heavy feeding, I would do a water change, about 30% to 50% with aerated RO water that was softer, acidic and slightly cooler than the current tank temperature, doing this routine usually got my Discus spawning...

HTH

I think that the environmental situation of the fish pond or fish tank is causing them to stop breeding. Some of the fishes might be suffering from one health problem or another which most likely will be casing them not to breed. I would suggest that you should check them out very well and determine where the problem is coming from. Also make sure to feed them well and properly and try cleaning out any dirt and debris from the pond.

I guess you have too many fish in your fish tank and your angelfish pair feel stressed and they will not pair anymore if they are agitated and their color changed this may be the problem.

Yeah. I guessed that your the place is too crowded for them and it caused stress to your fish. I might as well suggest that you observe the situation. You can experimentally separate those pairs and see if that works. Fishes are in general, become stressful in a crowded environment, especially angelfish.One thing also, is to avoid any disturbance when it comes to breeding season.