Playdough (homemade or store bought).  Multiple colors are not necessary.

Here is a homemade playdough recipe, if you would like to make your own.

2 cups all-purpose flour
3/4 cup salt
4 teaspoons cream of tartar
2 cups lukewarm water
2 Tablespoons vegetable oil (coconut oil works too)
OPTIONAL: FOOD COLORING 

Stir together the flour, salt and cream of tartar in a large pot. Next add the water and oil. If you’re only making one color, stir in the the color now.
Cook over medium-heat, stirring constantly. Continue stirring until the dough has thickened and begins to form into a ball. Remove from heat and then place inside a bowl, gallon sized bag or onto wax paper.
Allow to cool slightly and then knead until smooth. If you’re adding colors after, divide the dough into balls (for how many colors you want) and then add the dough into the quart sized bags. Start with about 5 drops of color and add more to brighten it. Knead the dough, while inside the bag so it doesn’t stain your hands. Once it’s all mixed together, you’re ready to PLAY.
Store the play dough inside the bags to keep soft. If stored properly it will keep soft for up to 3 months.