The Flute Suit is an outfit that Cake told Fionna to wear in order to impress Prince Gumball. Fionna sang, "This is my flute suit!" and played her flute. It made Prince Gumball crack up.
The hat is red with a green feather, and has holes for Fionna's hat. It has puffed sleeves that are red with orange stripes. The skirt is also red with orange stripes. The rest of the Flute Suit is orange. The Lyre Player wears a similar outfit.