Preheat Oven and Grease Pans:

Set oven to 350°F (175°C). Mist donut pans with non-stick spray.

Whisk Dry Ingredients:

In a large bowl, blend flour, baking powder, and salt with a whisk.

Mix Wet Ingredients:

In another bowl, mix buttermilk, sugar, eggs, butter, and vanilla; stir till uniform.

Combine Wet and Dry:

Slowly incorporate dry mixture into wet, stirring only until blended.

Divide and Color Batter:

Split batter equally among 4 small bowls. Mix a distinct neon color into each bowl until evenly tinted.

Layer and Swirl Batter:

Drop a spoonful of each colored batter into each donut cavity, then create a swirl pattern with a butter knife.

Bake and Cool Donuts:

Bake at 350°F (175°C) for 9-10 minutes, until a toothpick emerges clean. Let cool in pan for 10 minutes, then move to a wire rack to cool fully. Repeat with remaining batter.

Make Glaze:

For the glaze: In a medium bowl, whisk powdered sugar and milk until smooth.

Glaze and Sprinkle Donuts:

Position foil beneath the wire rack. Drizzle glaze slowly over donuts, covering tops thoroughly. Sprinkle immediately with unicorn sprinkles. Allow glaze to harden before serving.