Preheat the oven to 350ºF. Place muffin liners into the muffin pan and set it aside.
Whisk together in a small mixing bowl the flour, baking powder, salt, and sugar, set it aside.
Whisk together in a large mixing bowl the egg, milk, vanilla, and sour cream. Stir in the flour mixture just until it is combined.Combiine the wet iingredients ith the dry ingredients and set aside.
In a small mixing bowl stir together the sugar, cinnamon, and butter to create the swirl.
Fill the muffin liners so they are about 1/3 full. Sprinkle some of the cinnamon swirl mixtures on top of the batter. Top the mixture with more batter so the liner is 2/3 full, top it with more of the cinnamon swirl.
Bake for 15-20 minutes until the muffins are golden brown. Place the muffins onto a cooling rack.
While the muffins cool to combine the sugar and milk together to create the glaze.
Working with only 1 or 2 muffins at a time, drizzle the glaze on the muffins then sprinkle the yellow, purple and green sugar.