In a large mixing bowl, stir together the flour, salt, and cream of tartar.
Add the oil.
Heat the water to almost boiling.
Add the water to the bowl and stir until a dough ball forms. If the dough seems very sticky, more like a paste than a dough, then add up to ¼ cup more flour.
Once the dough is cool enough to handle, divide into 4-6 balls.
Add food coloring to each ball.
Gently knead the food coloring into the dough. As you mix, the color will distribute throughout the dough.
Notes
Food coloring can temporarily stain skin, surfaces, or clothes, so take care as you knead the color into the dough.
Store homemade playdough in airtight containers so it doesn't dry out.
This method is a no-cook playdough method; see post for how to make playdough on the stovetop.