I used 5 different colors.
TWO boxes of Knox Gelatin
One can sweetened condensed milk
Step One
Mix 3 packages of Knox gelatin in 1 1/2 cups boiling water.
Mix until dissolved.
Add sweetened condensed milk to Knox gelatin mixture.
Set aside.
Step 2
Mix 3 packages of Knox gelatin with 1 1/4 cups boiling water.
Mix until dissolved.
Set aside.
Step Three
Dissolve 1 box of Jell-O in 1 cup boiling water.
I started with blue because I wanted it on the bottom.
You can start with whatever color you'd like :)

Step Four
Add 1/4 cup of the Knox gelatin mixture to the Jell-O.
Pour into a 9x13 glass dish.
Step Five
Now the waiting begins!
Let set in the refrigerator for 20-30 minutes.
I did 20 minutes and my layers were perfectly set.

Step Six
Pour 3/4 cup sweetened condensed milk mixture over the Jell-O layer.
Step 7
Let sweetened condensed milk layer set up in refrigerator.
I let mine set 10 minutes and it was golden.
While I waited, I repeated Step 3 with the next color.
That way I was ready to add the next Jell-O
when the milk layer was set.

Repeat Steps 3-7 with the remaining four flavors.
Do not try to be speedy and use the freezer :)
My layer order was: blue, milk, green, milk, yellow, milk, orange, milk, redAnd VOILA!
You now have a beautiful rainbow Jell-O
to wow your friends and children :)
It can sit out of the refrigerator for up to three hours.
You can dig in with one big bite.