First off I'd like to say Artrage is by far the best painting app out there, I have them all and this is far superior to the rest so congrats!
Anyway, what I'd like to see when I first start a painting is a palette of standard oils, i.e. cadmium yellow, titanium white, sienna etc. all the standard oils I can actually buy off the shelf in an art shop. These would be a great starting palette to every painting and would enhance the authentic oil painting experience even further.
You may even be able to do this already, maybe I haven't found them yet? I've never been great with computers!
Keep up the good work, you've done a great job.