Prismatic Dress

 is an armor in. Upon completion of the The Rainbow Shell sidequest, the Rainbow Shell can be forged by Melchior into either three Prism Helm or one Prism Dress. If you have the Sun Stone, then he'll make some PrismSpecs (an accessory that greatly boosts damage).

Prism Dress can also be charmed by Ayla from the right hand of Queen Zeal. Additionally, Prism Dress can only be worn by Ayla, Lucca, and Marle.