In a bowl, dissolve blue gelatin in 1 cup boiling water; stir in 1 cup cold water. Add blueberries. Pour into 3 quart serving bowl. Refrigerate until firm, about 1 hour.
Meanwhile, in a saucepan sprinkle unflavored gelatin over 1/2 cup cold water; let stand 1 minute. Add cream and sugar; cook and stir over low heat until gelatin and sugar are completely dissolved. Cool to room temperature. Whisk in sour cream and vanilla. Spoon over blue layer. Refrigerate until firm.
In a bowl, dissolve raspberry gelatin in remaining hot water; stir in remaining cold water. Add raspberries. Spoon over cream layer. Chill until set. Garnish with whipped topping and additional berries if desired.