Preheat your oven to 350°F (175°C).
Grease a 9x5-inch loaf pan with butter or cooking spray.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking soda, baking powder, and salt.
In a separate bowl, mix the buttermilk, melted butter, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Fold in the rainbow sprinkles, reserving some for topping.
Pour the batter into the prepared loaf pan and smooth the top. Sprinkle reserved sprinkles on top.
Bake for 50-60 minutes, checking for doneness with a toothpick.
Allow the bread to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.