Preheat oven to 350°F (175°C). Grease and line three 8-inch and three 6-inch cake pans.

Whisk flour, sugar, baking powder, and salt. Cut in softened butter until coarse. Whisk eggs, coconut milk, and extract, then blend into dry ingredients until smooth. Divide among pans and bake 25-35 minutes. Cool completely.

In a saucepan, combine crushed pineapple, 1/2 cup sugar, and cornstarch. Cook over medium heat until very thick. Chill completely.

Beat 4 cups butter until pale. Gradually add powdered sugar, cream, and vanilla. Beat until fluffy. Divide and tint frosting into light, medium, and dark blue shades, leaving some white.

Level cakes. Build the 8-inch tier and 6-inch tier separately on cake boards, filling layers with pineapple filling. Crumb coat with white frosting and chill for 1 hour.

Frost both tiers with ombre colors (dark on bottom, light on top). Use an offset spatula to create wave textures while turning the cake.

Insert structural dowels into the 8-inch tier. Carefully stack the 6-inch tier on top.

Decorate with graham cracker 'sand', fondant palm trees, plumeria flowers, and edible pearls. Chill until 2 hours before serving.