It's a very good study, I like to see 'pencil lines' or what ever they are called in digital art
Thanks.
Well, indeed, lines are made with a digital brush which is intended to mimic a pencil. The name of the brush is "Pencil Hard". Well, it's hardly

a pencil, but it approximately resembles the feeling. For the colors, instead, I used some basic brushes, so basic that they cannot exist in nature. but they allow to block out the colors fast and then I used a bit of some brushes intended for blending, smearing or smudging. Nothing to demanding, just some brush whips in the right places.
Though, it is a starting point. I spent about 1 hour organizing some of the brushes in categories, unless I get lost. Usually, the official brush sets are already categorized, though, since it is an open source software, bundles from external contributors can be totally unorganized, undocumented, or poorly documented and you risk getting dozens of new brushes flooding like a tsunami in your palette. I believe there are more than 200 brushes in my installation (included some extra bundles I installed for curiosity). Most of which, I don't have a bare idea of what they do.
For instance, brushes in digital painting programs are actually small programs themself. These little pieces of program, are essentially simulators, that try to produce effects that mimic real world behaviors, very loosely. There are though limits caused by the time these programs have to compute something usable, which is the time of a stroke, cents of second or less. Also, no one have ever thought to simulate the paper and the medium. Watercolor, for example, to be simulated, wet on wet especially, would require a total redesign of the software.