Add 1/4 cup of the corn starch and 1/4 cup of coconut oil into a large mixing bowl. Mix together with a spoon until it starts to look like a smooth, buttery mixture.
Add the other 1/4 cup of corn starch to the mixture. Mix together with a spoon to form a dough. Pour the bubble bath on top. Mix with a spoon to combine all the ingredients.
The mixture now looks like a soft play dough. Scatter about 1 teaspoon of coloring on top of the ball of soap dough. Knead the ball with the coloring until it has an even color.