They're Blue, Da Ba Dee Da Ba Dai

Postcard credit: "Sappho Leaping Into The Sea From The Leucadian Promontory" (Théodore Chassériau, c. 1840).

Token: "Blue Lady" (Larry Elmore?, 1992), from Tales of The Lance, published by TSR.

Stickers:

• Paradise Killer, available from Black Screen Records.
• Cherry Moon Factory.

Card: "Blue Spruce" from Arboretum (2015), card game by Dan Cassar, published by Renegade Game Studios.