1. default paper color
   At the moment we can choose one of two: white or strong yellow.
   In my opinion, the yellow one is too strong - of course, this is just my opinion, but adding the possibility to choose a paper with a slightly less yellow color would be something great.
   I think the way to have a cool yellow color is in Notability. There yellow seems to be nicer - better perceived by the eye.

2. color of the application bar.
   Right now we have something like light navy blue - it's a bit sad and a very office color.
   Could you consider adding the ability for users to change this color?

I know these are, frankly, minor things, but adding the ability to change them could improve the look of the app.
These are my comments.