What a beautiful fish, I am so jealous. Black worms are bigger than the blood worms and are a true worm (I believe the bloodworms are insect larve) and marine fish go nuts for them, even picky eaters. The worms will die quickly in salt so you need to feed sparingly and the worms need to be fresh, live and clean. If you can find them they are just an awesome food.
All of the angels I have kept will generally go for fresh seafood, especially an opened fresh bivalve, if your fish is nibbling at flakes it will eat, just need to find something it likes.