01 - Combine warm water and sugar in a small bowl. Sprinkle yeast over the surface and let stand for 5 minutes until mixture becomes foamy.
02 - Mix flour, salt, and cinnamon in a large bowl. Add activated yeast mixture and melted butter. Knead by hand or with stand mixer for 8-10 minutes until dough is smooth and elastic.
03 - Divide dough evenly into three portions. Knead purple gel coloring into one portion, green into another, and yellow into the third until color is uniformly distributed throughout each section.
04 - Cover colored dough portions and let rest for 1 hour or until doubled in volume.
05 - Roll each colored dough portion into ropes approximately 12 inches long. Twist one rope of each color together, then form into bagel shape by pinching ends firmly to seal. Repeat process for remaining dough.
06 - Place shaped bagels on parchment-lined baking sheet. Cover and let rest for 20 minutes.
07 - Preheat oven to 425°F.
08 - Bring a large pot of water to boil. Add honey or sugar to water. Boil bagels two at a time for 1 minute per side. Remove with slotted spoon and drain on wire rack.
09 - Return boiled bagels to baking sheet. Bake for 18-22 minutes until golden brown. Allow to cool completely before glazing.
10 - Whisk together powdered sugar, milk, and vanilla extract until smooth. Drizzle glaze over cooled bagels and immediately sprinkle with purple, green, and gold sanding sugars while glaze is wet.