B.C.
Something beige or ivory would probably compliment the color of the dress.
I'd keep it small and not too elaborate - at least if it were for me - I don't have a lot of patience for large things on my head.
Something like this might work nicely:
https://www.amazon.com/Anita-Womens-fascinators-hairpin-f...
or
https://www.amazon.com/Valdler-Feather-flower-Fascinator-...