Preheat oven to 325°F and wrap outside of 9-inch springform pan with aluminum foil. Mix graham cracker crumbs, melted butter, sugar, and salt until mixture feels like wet sand. Press firmly into bottom of pan using measuring cup for even surface. Bake for 12 minutes, then set aside to cool.

Make blueberry swirl: Combine blueberries, sugar, and cornstarch in medium saucepan. Cook over medium heat, stirring frequently, until berries burst and mixture thickens (8-10 minutes). Stir in lemon juice, vanilla, and food coloring if using. Let cool completely.

Beat cream cheese until completely smooth to avoid lumps. Gradually add sugar, beating until fluffy. Add eggs one at a time, then mix in vanilla, sour cream, and flour until mixture is silky smooth.

Pour half the cheesecake batter over cooled crust. Drop spoonfuls of cooled blueberry mixture on top. Add remaining batter, then more blueberry swirls. Use knife to create marbled pattern without overmixing.

Place springform pan in large roasting pan and add hot water halfway up sides for water bath. Bake 55-60 minutes until center still jiggles slightly when shaken.

Turn off oven and let cool gradually with door cracked open for 1 hour. Remove from water bath and cool completely at room temperature, then refrigerate 4-6 hours or overnight.

Before serving, dust with powdered sugar and garnish with fresh blueberries if desired.