First, make the cake. Preheat oven to 350F and spray two 6" round cake pans with nonstick baking spray. In a small bowl, whisk together the ground flaxseed with the water and set aside to thicken.
In the bowl of a stand mixer, combine the flour, baking powder, baking soda, salt, and sugar.
Add in the vegan butter, and beat on low until it's incorporated and has a sandy texture.
In a small bowl, whisk together the oil, flaxseed mixture, nondairy yogurt, orange zest and and orange/vanilla extract, and add them to the dry ingredients. Mix until combined.
Pour in the unsweetened nondairy milk and orange juice, and beat on medium-low until smooth and creamy. Finally, gently stir in the blueberries
Divide batter evenly among the 2 pans, and bake for 45 minutes until cake is set in the center and a toothpick comes out clean.
When the cakes are completely cooled, you can make the frosting. In the bowl of a stand mixer, beat the shortening, vegan butter, and orange/vanilla extract together until completely smooth and creamy. Add in the powdered sugar, 1 cup at a time, until a thick frosting forms. Add in the salt.
To assemble the cake, divide the 2 cake layers in half to create 4 thin layers. Place one cake piece on your cake stand or platter, and spread some white frosting on top. Repeat with all.
To create the ombre effect, divide the remaining frosting into 3 bowls. Leave one of them white, add 1-2 drops of food coloring to the next bowl, and 5-6 drops to the last bowl. Add more or less until you reach your desired color.
Grab a large piping bag, and spoon in the darkest frosting, followed by the medium frosting, followed by the white. Pipe the frosting around the edges of the cake, starting at the bottom and working your way up. Using a bench scraper, smooth the edges of the cake.
For the top, spoon any remaining frosting in a piping bag fitted with a wide star tip (such as 1M). Frost swirls on top of the cake along the edge, and top each with a blueberry. You can fill the middle of the top of the cake with additional blueberries as well.
Serve immediately, or store in the fridge until needed.