I don’t have as much time for recreational drawing as I would like, but when I do I’m really having fun using my iPad. My app of choice these days is ArtRage, which has a “watercolor brush” tool that I like a lot.
As you can see, there is a lot of flexibility in how finished a piece one can choose to do. There’s no problem with just going and going and going and….until you have what you want.
I’ve also been trying various effects on iPad drawings and some of my photos using Camera Awesome, which has a lot more options than Instagram and works with any photo on a Camera Roll no matter what camera app you use.