This is a custom ZBrush Renderset I created that gives the feel of a colouring book or sketch.
In the last image I've removed the white background in Clip Studio Paint (any photo editing or art software will do) and set the blending mode to "brightness" to turn the grey shadows closer to the blue background.
Place the .zrp file into: Program Files\Pixologic\ZBrush ('version')\ZRenderPresets and it should be available next time you open ZBrush.
This renderset is free to use for both personal and commercial work.
Hope it's helpful and feel free to tag me @scoutwindsor with your awesome renders!
.ZRP ZBrush renderset file