Making your own colored play dough is actually very easy to do. The base recipe for basic dough that we use comes from Little Acorn Learning. You can find it on the blog post of Eileen's, dyed a lovely Valentine pink ---> HERE.
Basic Dough Recipe
2 Cups flour
4 T cream of tartar
2T cooking oil
1 C salt
2 Cups boiling water (I just use hot water from the coffee maker)
Put all ingredients except water in a large bowl. Pour water over the mix and stir it with a spoon. Knead it with your hands (careful! Its hot!) and maybe add a little more flour if it is too "soupy" ... keep at the kneading until it is the right dough consistency. Store in an air tight container (we keep ours in the fridge and it lasts for a couple of months)
When you mix up the basic, no-color version of the dough you get approximately 3 Cups of Dough "Blanks"
Divide the dough into equal amounts for each color that you want to make. We wanted a rainbow so we divded our dough blanks into 6 roughly equal balls.
Sprinkle the KoolAid packet of your color choice on top of your dough ball and mix it up by hand, kneading and kneading until all the Kool Aid powder is worked into the dough and it changes color! Voila! That is easy peasy, isn't it?
Now, a word of caution:
Darker colored KoolAid, like Berry Blue, will stain your skin if you make direct contact with the powder. So, unless you want to be all Smurfy like me, wear gloves when kneading you dough blanks!
Also, while I have not personally noticed that any of the already kneaded ready-for-play dough stained anything or anyone at our house, your mileage may vary, and I don't want anyone mad at me when they accidently dye their carpets or their toddlers Berry Blue. So lets all make the Laundry Fairy happy and err on the side of caution - wear clothes you can get dirty in and put down a mat on the floor, okay?
Now, back to the colors ...
You could also use Grape for purple - my experience with dying play silks with grape KoolAid is that it makes a very dark purple.
We store our play dough in a plastic container with a lid and keep it in the fridge. We made a batch last fall that lasted until almost Christmas. It will dry out eventually but when it is this easy to make more, who cares?