Lots of great ideas. I love that you didn't opt for baby pink for a girl. With the brighter colors, she will use and treasure this one for her whole life!
Being that I am the person who seems to always get the project finished the night before it's due, I'd go for the 2 color flange, narrow yellow with wider darker blue tone fabric. Hopefully, close to colors from the center!
Whatever you choose to do, this is a beautiful quilt and going to one lucky girl!