You cant play in official tournaments without sleeves, but there are official sleeves with the same art as card backs
Armed with a clear window, and a great shuffle feel, Dragon Shield sleeves come in a huge variety of colours to bling out your deck
This is the same wedding dress that Yuna wears during her marriage to Seymour Guado in Final Fantasy X
Its definitely worth looking into if you havent played it before
Decks can be made up of any two colors, but the three pairings that make up the starter decks are Sapphire/Steel, Ruby/Emerald, and Amber/Amethyst
But honestly, there is only one possible capstone to this archetype, one card that hearkens back to the origins of the name for this type of deck