Hi June,
I found this in a jello cookbook. In the picture the layers with the sour cream are not white as you mentioned, but a pretty pink and soft creamy green. The recipe also didn't mention nuts, but you could certainly add them, either to the jello layers or the creamy layers.
I have two jello cookbooks and this is the only recipe I found that is close to what you are looking for. I also have one for a Rainbow Ribbon, which is done similar to the Christmas Ribbon and uses 5 different flavors of jello. If you would like the instructions for that let me know.

Christmas Ribbon

2 (4 oz. each)pkgs.strawberry jello
2 (4 oz. each) pkgs lime jello
5 cups boiling water
2/3 cup sour cream or plain or vanilla yogurt

Dissolve strawberry jello in 2 1/2 cups of the water.Pour 1 1/2 cups into a 6 cup ring mold. Chill until set but not firm, about 30 minutes.

Chill remaining gelatin in bowl until slightly thickened, gradually blend in 1/3 cup of the sour cream or yogurt. Spoon over gelatin in mold. Chill until set but not firm, about 15 minutes.

Repeat this process with the lime jello, remaining water and sour cream. Layering as with the strawberry jello.
Chill at least 2 hours. Unmold. Makes 12 servings.