|Digital value plan with markers|
in Paper by 53 app
However, you will never run out of ink, paper or pencil if you choose the digital app, Paper by 53.
The rewind feature is one I wouldn't mind using on a few of my paintings. :)
For a "real" planning sketch like this, I use Prismacolor or Copic Markers: 30% warm grey, 60% cool grey and black in my Robert Bateman sketchbook.