I just got back from a trip and came across this hat in Elias & Co in California Adventure:
It's navy blue with a yellow D. Is this what you were looking for?
Anyway, I thought of this thread when I saw it so I snapped a quick photo and made sure to remember where I saw it. I hope this helps!
I saw the same hat, as well as a white hat with a Blue "D" in several places. I saw that hat in several color schemes at the shop in the midway at Paradise Pier and at the Emporium in Main street last week while I was there.