This reef butterfly fish
      has got blue and yellow diagonal stripes on its sides.

Imperor angelfish

( Pomacanthus imperator )

I saw this fish only two or three times. It is not so common in Sharm el Sheikh. Like butterflyfish this fish has got a black mask with a light-blue edge. Body coloring is unusial - blue and yellow diagonal stripes. Blue color occurs not so often at reef.