In a microwave-safe bowl heat 1 cup of water for 2 1/2 minutes (until boiling).
In a large bowl add flour, salt, cream of tartar, and one 3 oz packet of Jell-O. Stir to combine.
Carefully add the boiling water and oil to the flour mixture. Stir until all ingredients are well combined and dough begins to form. If the dough is still sticky, add 1-2 Tbsp of flour at a time, and mix well until the dough is no longer sticky.
Place on a piece of parchment paper until the dough is completely cooled.
Repeat steps 1-4 until all the Jell-O rainbow colors are made.