If you are a V.I.B. for Sephora, you can get this app for free, which is how I ended up downloading it. If you aren't, than this app will cost you $2.99, but it is worth it. This is the coolest doodling app that I have found. You can download it at the app store here.
You can choose a single color or mix two and make generative art work with the swipe of a finger.
Here is just a sample of what you can create. Hint: You can also save your work and upload it. No Master's Degree required to be an art god.