In a medium saucepan, boil milk and sugar. Cool completely, but do not refrigerate.
Dissolve each package of flavored gelatin separately in 1 1/2 cups of boiling water. Set aside.
Dissolve unflavored gelatin in 1/2 cup of warm water. Add with sour cream to cooled milk and sugar mixture. Set aside.
Spread gelatin of one color on the bottom of a 9x13 inch pan. Chill in refrigerator until set. Then put 1 1/3 cup of the sour cream mixture on the chilled, firm layer of gelatin. Keep alternating these until all gelatin is used. Be sure to chill after each addition of gelatin.