BillFinn-
I saw the show last night and these were the things that I believe make Elena stand out as Clara, and what Fabrizio notices.
The wig does have quite a bit of blonde highlight which really shimmer, especially when you see her from the back. It's lighter in contrast to David's/Fabrizio's hair and the hair/wigs of the rest of the family.
Elena's skin tone is not nearly as dark as David's and his lines about her skin being white as milk ring true as Fabrizio struggles with the right words and his awe of her skin.
Elena has blue eyes, not brown like Fabrizio and his family. I think they stand out even more because she has darker hair.
Whatever the hair color, her overall look in that first scene that Fabrizio sees her is striking, and you have no problem beliving that she has truely caught his eye...both with her physical beauty and with the look of wonder she has as she is looking at her surroundings...and you see that in Fabrizio's eyes as well. AND, on top of it all...and best of all...Elena gives a wonderful performance as Clara. Her voice is gorgeous, and she is a fine actress.
"If there is to be any peace it will come through being, not having."
Henry Miller