Coral Beauty, along with most Dwarf Angelfish are primarily algae eaters, though they do also eat some meaty foods. Algae should be the majority of it's diet. Dried Nori or Spirulina sheets, in red and green, should be fed. If you have any live caelurpa, it might induce it to eat. Live Ulva is also a very good choice and will usually be eaten by finicky algae grazers.
I also agree on the suggestion of frozen Rod's Food. I haven't found a fish yet that won't devour it!