Combine one package of flavored gelatin and one envelope of unflavored gelatin in a bowl. Stir in 1 cup of boiling water until dissolved. Pour into a dish coated with nonstick cooking spray. Refrigerate for 20 minutes.
Combine a can of sweetened evaporated milk and 1 cup of boiling water in a bowl. Sprinkle two envelopes of unflavored gelatin over 1/4 cup of cold water in another bowl. Let stand for 1 minute. Stir in 3/4 cup of boiling water. Add to the milk mixture. Pour 1 1/4 cup of the creamy gelatin mixture over the first flavored gelatin layer. Refrigerate about 25 minutes.
Repeat from beginning of recipe twice, alternating flavored gelatin with creamy gelatin layers. Chill each layer 20-25 minutes before pouring the next layer on top. Make final flavored gelatin. Spoon over top. Refrigerate for at least 1 hour after completing last layer before cutting into 1 inch squares.