Preheat the oven to 325 degrees F. Spray a donut pan with cooking spray, use a paper towel to lightly spread/remove excess spray.
In a large bowl, combine the flour, sugar, baking powder and salt. In another bowl, combine the milk, eggs, vanilla, and oil. Stir the dry ingredients into the wet ingredients, mix just until combined.
Transfer the batter to a large piping bag or use a ziploc bag with one corner cut off. Pipe the batter into the donut pan, filling each donut hole about 2/3 full. Tap the donut pan against the counter to release any air bubbles.
Bake the donuts for 10 minutes, or until a toothpick comes out clean. Remove from the oven and let the donuts sit in the pan for 5 minutes before moving to a wire rack. Allow the donuts to cool completely before moving on.
Melt 1/3 bag of the white candy melts. They can be microwaved or you can melt them on the stove top, whatever your preference. If microwaving, place each color (about 1/3 of the bag) in a microwave safe bowl and melt one color at a time. I like to start with 1 minute at 60% power, then stir and another minute at 60% power and stir again. Allow the candy melts to cool for about 5 minutes.
Transfer the melted white candy into shallow bowl that will easily allow you to dip the donuts into. Dip each donut, allowing the excess to fall off. Place the donuts on a cooling rack and allow them to harden.
Melt the blue candy melts (about 1/3 to 1/4 of the bag) and allow it to cool for 5 minutes (otherwise it might be too runny). Transfer the blue candy melts into a small squeeze bottle and draw the blue corners onto the donuts. Use a toothpick to help spread out the blue chocolate.
Melt the red candy melts (about 1/3 to 1/4 of the bag) and allow it to cool for 5 minutes (otherwise it might be too runny). Transfer the red candy melts into a small squeeze bottle and draw the red stripes across the donuts.
Once the blue corner is semi-set, transfer a small amount of white candy melts into another squeeze bottle and add the white polka dots to the blue corner. Allow the candy melts to harden completely. Store in an airtight container.