The Koran has flat light blue and white lines in semi-jagged patterns.
The Emperor has more detailed, curvaceous white lines that fluoresce very bright blue as the fish turns away from the viewer. I watched an Emperor Angel for about 20 minutes one day. The blue light is mesmerizing. They are truly one of the most beautiful fish I've ever seen.
Here's some blurry pictures I took of a teenage Emperor. The grey base color and black dots are signs that it's about halfway to getting its Adult coloring.
Picture 1
Picture 2
The fluorescence could be done in much the same way as the Royal Gramma's reddish-orange sheen when the fish turns.
I definately think they are distinct enough to warrant having both in the Aquarium. Jim has said that the lines are too detailed on an Emperor and would break up when the fish turns to the side.