I stopped by this afternoon to check and see when the church was open (my guidebook said mornings only) but in fact it was open and a pleasure to see. Two lovely women greet you (neither distracted on telefonino as is often typical) and help you!
I had a number of questions about the lovely little chapel - such as: Why are the domes painted red? They were able to answer me - in English even - and say that a small pink swatch of paint was found in the 19th century by the person restoring the church then and from that, the idea came that the domes had originally been painted red. In fact, they said, this is wrong - the domes were originally painted white. At any rate, it's pretty amazing that they haven't repainted it to WHITE. In addition, the other church - St. John of the Hermits - with red domes was painted in response to the same 19th century mistake. Now the red seems so iconic. And yet...I hope one day they will paint the domes white.
In addition there is a small book about the church (written in a very archaic and convoluted text, but at least there IS a book) available for sale of 2.5 EU which says that they believe the walls would have been covered with mosaics.
The feeling is quite lovely inside. I had to ask about The Knights, as well.
To me, this kind of Arab-Norman architecture is what is most unique about Palermo and what I look forward to reading up about when I get home from my trip.