Stir together yeast, 1/2 cup warm water, and 1 Tablespoon sugar and let stand 5 minutes until foamy.
Melt Butter. Combine sour cream, sugar, melted butter, and salt and beat together until smooth.
Beat sour cream mixture, yeast mixture, eggs, and 2 cups flour at medium speed with a heavy-duty electric stand mixer until smooth. Replace paddle on mixer with a dough hook, reduce speed to low, and gradually add enough remaining flour (4 to 4 1/2 cups) until a soft dough forms.
Once dough comes together increase speed to medium and mix 5-7 minutes until dough is smooth and elastic. Place in a well-greased bowl, turning to grease top. Cover and let rise in a warm place (85°), free from drafts, 1 hour or until dough is doubled in bulk.
Punch down dough, and divide in half. Roll each portion into a 22- x 12-inch rectangle. Beat 3/4 cup sugar, cream cheese, 1 egg, and vanilla at medium speed with an electric mixer until smooth. Spread cream cheese mixture evenly on each dough rectangle, leaving 1-inch borders.
Roll up each dough rectangle, jelly-roll fashion, starting at long side. Place one dough roll, seam side down, on a parchment lined baking sheet. Bring ends of roll together to form an oval ring, moistening and pinching edges together to seal. Repeat with second dough roll.
Cover and let rise until doubled in bulk.
Bake at 375° for 14 to 16 minutes or until golden. Slightly cool cakes on pans on wire racks (about 10 minutes). Drizzle glaze evenly over warm cakes; sprinkle with colored sugars, alternating colors and forming bands. Let cool completely.