I recently decided to spruce up a bit of "finger painting" code I posted to the code exchange 2 years ago so that it is Graphics 2.0 compatible, and turn it into a module so that you can add it to an existing Corona project with just one line of code. I'm pretty pleased with the results. The code is free to download, modify, and use as you see fit. You can read about it and download fingerPaint.lua or a sample app that shows it in action at http://www.jasonschroeder.com/2014/03/21/finger-painting-in-corona-with-....
Here's a video preview of how it looks in use: https://www.youtube.com/watch?v=K6smKu44UBk
The sample app (seen in the video) also makes use of a colorPicker library I'm pretty proud of that I'm going to make available next week on my site. Hope it comes in handy for some of you! :)