Created (quickly) in Clip Studio Pro. Fast paint process (some might call it the lazy man process). I go directly from the pencil sketch to using the auto color feature to lay paint across the entire canvas in one deft move. Then just refine the picture a bit with the airbrush and oil paint tool.
Here’s a process video uploaded to YouTube. Roughly a 20 minute drawing, but had to play back at 1.5x speed to reduce it under 15 minutes.